The method (derived from one in USEPA SW-846: http://www.epa.gov/epaoswer/hazwaste/test/pdfs/chap9.pdf - good discussion on page 9-6) is designed to estimateMessage 1 of 2 , Jan 30, 2006View Source
The method (derived from one in USEPA SW-846: http://www.epa.gov/epaoswer/hazwaste/test/pdfs/chap9.pdf - good discussion on page 9-6) is designed to estimate the number of samples from a homogeneous, normally-distributed population needed to determine if the mean value of the population is less than some regulatory limit, with a stated level of certainty (80% in this case).
It’s not a bad tool for that task, but make sure what it’s answering is what you’re really asking. Are you interested in the mean value of the pile or the likely maximum value? Is it reasonable to expect the pile’s concentrations to be normally distributed? Is the pile homogeneous and amenable to being sampled in this way?
Of course, you may be forced to use this for at least two reasons:1) regulatory requirement or 2) nothing better.
To me, it’s much safer to use the rule of thumb that you take at least 10 – 20 samples in every “block” you consider homogeneous. This generally gives you enough statistical power to estimate most anything needed for investigation. When in doubt – consult a good statistician who is familiar with environmental sampling (not all are!).
Senior Environmental Scientist – Geochemistry (and statistics!)
MACTEC Engineering and Consulting, Inc.
Kennesaw , Georgia , USA
From: Robert Pope [mailto:rpope@...]
Sent: Friday, January 27, 2006 2:39 PM
Cc: AI Geostats mailing list; Robert Pope
Subject: [ai-geostats] SAM Manual Stockpile Statistics Worksheet
I am writing with a specific question about the County of San Diego Site Assessment and Mitigation Manual (SAM Manual).
In Section 5, Page 5-75, Table 5-13, they offer a Stockpile Statistics Worksheet that is designed to estimate the minimum number of samples required to sufficiently evaluate a stockpile of waste soils.
1) Does anyone have opinions about the method they utilize? (i.e., is it good/bad and why?)
2) Does anyone have a better method?
Waterstone Environmental, Inc.