May 22, 20234 min read

8. Land Partition: Step 2

Site Plan

After the hydrogeology review was underway, I needed to start planning where the proposed property lines would go and calculate how big our new lot would be. The zoning of our area requires a minimum lot size of 2 acres, which would be no problem with the space we have to work with. I had some idea of where the new property lines should be, but there was no drawing or survey on county record to work from. It would have been almost impossible to accurately measure our property lines with a measuring tape.

We hired a surveyor to create a site map of our entire 6 acres. The surveyor came out to the site and located monuments (property pins) at the property corners. In our case, the monuments were pieces of rebar buried in the ground.

The surveyors used complex equipment to triangulate the property corners and record their location/dimensions. Later, the data was converted into a site map as shown at the top of the page.

This initial site map was critical in the early planning stages since a detailed site plan was required as part of the partition application. I was able to take the surveyors drawing and import it into my CAD drawing software to map out locations and features for our development. We used the site plan to communicate questions to county officials, request quotes from well drilling vendors, review geotechnical engineering plans, and discuss property layout with design firms. You can see the evolution of our site plan below as it starts from only having proposed partition lines to full detail with house and driveway locations.

Site Evaluation for Septic

According to the county website, next on the to-do list was the septic site evaluation. This is the process of determining if a particular property is acceptable for the installation of an onsite wastewater disposal system since a city sewer is not available. The purpose of the evaluation is to locate suitable soils in an area that is large enough for both the initial drainfield area and the replacement drainfield area. In other states, this process would be similar to a “perc test”, although in Oregon, they don’t actually perform a percolation test.

Here are some of the site features that are considered during a site evaluation:

-Soil types; how well they drain and other evidence of good soil structure for treatment

-Depth to evidence of high groundwater

-Wells located on the site or adjacent sites

-Slopes, escarpments, ground surface variations, topography

-Creeks or springs on the site or adjacent properties

-Whether the soils have been disturbed

-Setbacks from property lines, buildings, water lines, and other utilities

-Other site features that could affect the placement of your on-site system

The first order of business was to determine test pit locations. The county website says you need at least 2 test pits in the proposed drainfield locations approximately 75 feet apart. I knew where we wanted place the house, and in order to have the simplest type of septic system, the tank and drainfield needed to gravity flow away from the house. The area behind the house was the most suitable location because of the gentle downhill slope. However, part of the slope is in a drainage swale which had me second guessing this plan.

Drainage/water & septic systems don’t mix, so I was worried this would not be an ideal location. I called a handful of septic installers and asked for installation quotes and to recommend a location for the drainfield. 4 or 5 contractors visited our site and recommended the same area as I had been thinking about. They thought there was plenty of room to place the drainfield and stay out of the swale.

I walked the area and painted an “X” on the ground in the 2 locations where I thought the test pits should be (there was really no science behind this, I just picked a random spot in the area which was about the size of half a football field). The professionals had suggested placing one additional hole in a different location on the property just in case this area was rejected. Test pits are shown on the site plans above and in the pictures below.

In March, we had snow and rain, but I was determined to keep moving forward. I rented an excavator and started digging. Following the county’s instructional drawing, I dug three holes, 5 feet deep and 2 feet wide. Foolishly, I rented a 12” wide excavator bucket instead of a 24” bucket which made this process so much harder than it needed to be.

Once the holes were dug, I submitted the application to the county and they said we would get a call to schedule the inspection. Several weeks later, the inspector came out to the site and completed the evaluation. She climbed down into the hole to examine each layer of material and record the depths. The inspector judged the color of the soil, texture, amount of rock fragments, and clay content. She made the call right then and there that we would be approved for a standard gravity flow system with 450 linear feet of drainfield. This was terrific news. If the soils were not suitable for a standard system, we would have had to install an alternative treatment septic system which are very expensive and difficult to maintain. Here is the completed site evaluation: