The TCEQ has soil sampling requirements for Texas Land Application Permits (TLAP’s) which varies in scope from site to site. Over the past four years there have been many clarifications and additional requirements added to permits when they are up for renewal or amended at any point. The vast majority of Municipal WWTPs are now required to sample annually at three depths: 0″-6″, 6″-18″, and 18″-30″ and for the parameters shown in the table below. The TCEQ requires that sampling is performed during the winter months (December, January, February) because it is the time of the least biological activity. Winter marks the end of one growing season and the start of another. It is an opportune moment to establish the baseline of what underlying conditions should be addressed before the spring growing season arrives.

 

PARAMETER	UNITS
pH	SU
Electrical Conductivity	mmhos/cm
Nitrate-N	mg/kg
TKN	mg/kg
Total Nitrogen	mg/kg
Sodium Absorption Ratio (SAR)	ratio
Plant Available
Phosphorus	mg/kg
Potassium	mg/kg
Calcium	mg/kg
Magnesium	mg/kg
Sodium	mg/kg
Sulfur	mg/kg
Water-Soluble
Sodium	mg/kg
Calcium	mg/kg
Magnesium	mg/kg

 

These parameters primarily measure the fertility of the soil and are an indicator of crop health. The Sodium Absorption Ratio (SAR) in particular is an important metric. SAR is a widely used index for characterizing the soil sodicity, which affects crusting and soil permeability. Not everyone is required to sample for SAR, but if you are, be sure to check out the article I’ve written specifically on SAR and how it pertains to costly gypsum amendments.

Your permit will tell you how many sites you must sample at depending upon the size of your irrigation area. Typically, the requirement is a minimum of 1 Site/80 Ac. This means that an irrigation tract with 160 Ac. of application area will need to sample at at least 2 sites. Simply by adding 1 more Ac. to make the total 161 Ac. would require 3 sampling sites! This is one of the many small considerations that I take into account when sizing the phasing of a permit, and that’s because soil sampling is not easy!

For each site that you’re required to sample at, a composite sample must be made. The composite sample should be made from at least 10-15 separate sub-samples pulled from within a relatively short distance of each other and representing the same general crop and subsurface conditions. So, in our example of 3 sites, this means that at least 30 holes must be dug to a depth of nearly 3ft. This is a substantial physical task to demand of any operator, as well as a considerable time drain away from important work at the treatment plant.

Your TCEQ Region Field Office looks closely at your soil sampling data each year and tracks historical data to look for trends.  In my experience, most operators aren’t reviewing their historical data and looking for trends. I strongly believe that they should be. A red flag at the TCEQ Field Offices could initiate anything from more sampling requirements, increased reporting, or even enforcement actions. If you’re unsure of where your soil health stands please do not hesitate to reach out for consultation.