pH Meter Calibration For Industrial Stormwater Sampling

Industrial stormwater sampling is a key requirement of the new CA stormwater permit. Learn how to measure pH to ensure accurate analytical results.

Many sites struggle with pH meters when stormwater sampling because they see pH meter calibration as really difficult. In California, all the Level 1 Exceedance Response Action (ERA) evaluations and reports we did as Qualified Industrial Stormwater Practitioner (QISP)s for pH exceedances resulted in recommendations of increased pH measurement training and the use of a pH meter. To help out our customers, we reiterate what we have gone over in training sessions, and to help other companies, we put together the basics on pH monitoring including a sweet video on how to calibrate a pH meter….it is not too hard. Really.

pH is measured on a numeric scale in standard units (SU) to specify the acidity or alkalinity of an industrial stormwater sample. Samples with a pH less than 7 SU are acidic and samples with a pH greater than pH 7 SU are alkaline or basic. The analytical method for pH only allows 15 minutes between collection and analysis. This means samples are measured on site using either a pH field meter or litmus paper. In the video below, Mapistry’s Environmental Services Manager, Amber Smith, walks you through an easy pH meter calibration process for an  Oakton EcoTestr pH meter (nope, we don’t get a commission or money from them…we just like it for the price ~$50).
Samples are usually measured in unpreserved, polyethylene (aka plastic) bottles, although glass bottles are also acceptable. To learn more about the other analytes you as an industrial facility measure for, such as total suspended solids (TSS) and oil and grease (O&G), check out our previous  post looking behind the scenes at an analytical laboratoryRemember: Do not measure pH of a sample collected in a container being used for TSS or O&G, so as not to cross-contaminate samples.
Wistia video thumbnail


Litmus Paper

Litmus paper can be used to measure pH only sites that are not in Exceedance Response Action [ERA] Level 1 status , or if a site is subject to Subchapter N Effluent Limitation Guidelines (ELGs). Keep in mind that allow litmus paper is allowed under many permits, it can be difficult to read and can cause erroneous readings. In California, all the Level 1 ERA evaluations and reports we did for pH exceedances resulted in recommendations of increased pH measurement training and the use of a pH meter. The reason that they went into Level 1 was likely to incorrect readings of litmus paper (see below how close pH 2, 3 and 4 SU are in comparison to the litmus paper with a sample) and/or bad litmus paper. All industrial facilities should consider using a pH meter for their stormwater sampling or at the very least have it as a backup if the sampler reads pH less than 6 SU or greater than 9 SU, which are the instantaneous numeric action levels (NALs) for pH in California.

Calibration Documentation

Remember that pH measurements must be taken within 15 minutes of sample collection. Therefore, calibrate your pH meter before you head out to sample and enter it in pH calibration log. Mapistry’s software makes logging this easy and keeps it in an auditable location, accessible to the entire staff. If you would like to learn more about how Mapistry can make it easy to keep track of when you have to sample and notify you when you are in danger of exceeding NAL’s, schedule a demo today


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