Updated: Oct 16, 2018
Every Pinelands Commission application for development needs to be concerned with groundwater levels, if the property is not served by a public sanitary system. While the only way to truly determine the seasonal high water table (SHWT) is by soil sampling conducted by a scientist, the United States Department of Agriculture (USDA) has a website that will give you useful information to glean an educated guess.
Under the Water Quality Standards of the Pinelands Comprehensive Plan, the depth to seasonal high water table needs to be at least five feet for homes served by septic systems. That is, to meet water quality standards, ground water cannot be encountered within five feet of the natural grade of the land. For quick sampling, soils scientists use hand augers to examine the soil below the surface.
Groundwater levels fluctuate by season and from year-to-year. They rise and fall depending upon annual precipitation and time of the year. Generally, with the melting of the snow in March, water levels rise. And they fall during late summer, when trees and plants require more hydration.
Since the water table changes over time, it would be inaccurate to dig until you hit water on any given day. Scientists, therefore, want to find historical information, so they study the soils. When done properly, the soils reveal historic water saturation, which indicates the high water table – even if you dig during the driest month of the year.
Soil with historical water saturation becomes mottled, which means it becomes streaked and blotchy with shades of gray. Water-logged soils are starved of oxygen, lose their rich red and brown colors and show grayish mottles.
The Pinelands Commission defines "seasonal high water table" as “the level below the natural surface of the ground to which water seasonally rises in the soil in most years” (emphasis added). Notice the definition states “in most years”. I have witnessed heated discussions about shades of gray, because this is not an exact science.
Should you decide to proceed with a development application involving a septic system, the Pinelands Commission will require that a qualified soils scientist conduct a soil sampling to determine the SHWT. The Commission will also require a soils log, which will list every soil type encountered during the dig. Different soil types will be recorded at each depth observed.
Before you submit an application and spend money, however, you should make a public records request and make an educated guess concerning the SHWT. The best way to determine the likely SHWT on a plot of land is to know the soil type. Each soil type has an estimated SHWT.
The US Department of Agriculture (USDA) provides an online portal covering the soils for 95 percent of the counties across the country. Let’s look at a parcel of land on the west side of North Shore Drive, in Williamstown, New Jersey. Here are the steps to follow:
2. Click the green (surrounded by gray) button at the top of the page. The button is imprinted with the letters “WSS” for Web Soil Survey.
3. On the left-hand side, you will find a navigation bar entitled, “Quick Navigation”. Click on “Address” and punch in “North Shore Drive, Williamstown, New Jersey” and click “View”.
4. Click the hand symbol below the title, “Area of Interest Interactive Map”, to scroll the aerial photograph to your desired location.
5. Click AOI (Area of Interest) tab above the photograph and, while pressing down on control pad, outline the area that you want to examine. Once you do, the AOI will populate with a blue striped square or rectangle.
6. Next, click “Soils Map” on the very top horizontal navigation bar. The map and soils overlay will appear with symbols for the different soil types.
7. On the left-hand side, you will find a “Map Unit Legend”, which lists the soils types found on the map.
8. To examine the characteristics of each soil type, click on the hyper-link associated with the soils found.
9. Under “Properties and qualities”, you will find the depth to water table.
In this example, on North Shore Drive, according to the USDA, the area of interest contains Atsion Sand (AtsAr) and Manahawkin Muck (MakAt) soils. The estimated SHWT (depth to water table) for these soil types are 0 to 12 inches and 0 to 6 inches, respectively.
This tool is not foolproof. It is like wetlands mapping – about 80 percent reliable. However, it is free and a good starting point for assessing ground conditions. Again, the only conclusive means of determining the SHWT is by having a qualified soils scientist examine samples.