Land owners looking to subdivide existing parcels should understand the soil testing process as well as management areas and their significance. All of the soils within our county are considered seasonal soils, meaning they have a fluctuating seasonal water table. Some fluctuate more than others.
Even soils that are considered well drained, or having seasonal high-water tables between 4 to 6 feet or more, can still have significant surface silt or clay in our area. The silt and clay affect the soils percolation rate. Soils are required to meet a percolation rate of less than 60 minutes per inch in the upper soils. A percolation test is a test to determine a soils absorption rate, hence the term “perc” test.
The “wet-season” in Worcester County is whenever the majority of the county’s 16 monitoring wells are within 0.5 standard deviation of the wet season mean. Typically, this falls between November to May. It may not be “in-season” during that whole time and never has been, but it fluctuates. The county’s monitoring wells are always read along with a particular site project as a comparison. The county wells have been monitored for 20-30 years, so data is well established.
In soils with water tables closer to the surface, the management area of the county becomes important. In an “A” management area, a minimum two-foot treatment zone is required and preferably greater. This is where moderate to well drained soils are needed.
In a “B-1” management area, a one-foot minimum treatment zone is required for a standard system and two-foot for a sand mound system. In this management area, moderately drained soils can meet the requirements in most cases unless a percolation rate of less than 60 minutes per inch cannot be achieved.
In a “B-2” management area, a zero foot treatment zone is the minimum requirement allowing for hydraulic conductivity testing. Considering that 80% of Worcester County soils are hydric (less than a one-foot seasonal water table), the “B-2” management area allows for some of those soils to support sewage disposal. If at least a one-foot water table is achieved seasonally, then as long as the water-bearing sands below meet a hydraulic conductivity rate between 2-13 feet per day, the site can be approved. The system design in this case would be an elevated sand-lined trench to enable the wastewater to have enough head pressure to get down to where it can drain away.
Lauren Bunting is a Broker with Keller Williams Realty of Delmarva in Ocean City, Maryland.
