2025-10-27 – Weekly Hydrology News : Why three pre-rinses in fieldwork?

Last week, the hydrology forum was buzzing with thoughtful exchanges on improving fieldwork practices and job opportunities. Members delved into the rationale behind multiple pre-rinses during field sampling, while others debated the longevity and effectiveness of low-cost sensors. The community also shared insights on the latest job market trends, highlighting early career opportunities and the increasing demand for hydraulic experts.


This Week’s Hot Topics

Why we do three pre-rinses in the field
A detailed discussion on the importance of thorough pre-rinses to prevent sample contamination. It’s a reminder of fieldwork’s meticulous nature.
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2025-10-24 – Weekly Hydrology Jobs: Early Career Opportunities in Hydrology
A roundup of job openings, perfect for those starting their hydrology careers or looking to pivot.
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First-flush storm samples and QC
This thread explores techniques to ensure quality control in first-flush stormwater sampling, a critical aspect of stormwater management.
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Where Are the Best Places to Find Hydrology Jobs?
Members share insights on the most effective job-hunting strategies and locations within the hydrology field.
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Low-cost sensors that actually last
A practical discussion on durable, cost-effective sensors that can withstand harsh environmental conditions, crucial for ongoing field studies.
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Dialing in crest timing before alerts
This topic covers the technological advancements in predicting flood crest timings, a vital part of flood management systems.
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Would You Take This Job? – Sr. Hydrologist and Hydraulic Engineer
A candid look at a senior-level hydrology job offer, sparking conversation about career growth and professional challenges.
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2025-10-16 – Weekly Hydrology Jobs: Demand for Hydraulics Experts Soaring
An overview of the rising need for hydraulic expertise in various sectors, with a focus on immediate job openings.
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Where does water linger the longest
Exploring the dynamics of water retention in different environments, this thread offers valuable insights for water resource management.
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Would You Take This Job? Hydrology & Hydraulics Engineer - Land Development/Public Infrastructure
A critical discussion on a job opportunity in land development and public infrastructure, weighing the pros and cons.
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Looking forward to another week of valuable exchanges. Keep contributing your expertise and questions!

On wells and streams, I only stick with “three pre-rinses” if the waste-rinse EC is still drifting — once the second rinse matches ambient within about 5%, I sample to save time and spare those low-cost sensors. Small caveat: I never pre-rinse PFAS bottles or any containers with preservatives. Anyone else logging rinse EC instead of counting rinses?

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If time’s tight, I swap the ‘three pre-rinses’ rule for one pre-rinse plus purging about one to two tubing volumes until specific conductance and turbidity plateau for a couple minutes… For trace metals, I still do three because acid-washed surfaces need conditioning; for nutrients I haven’t seen a benefit beyond one. From last week’s low-cost sensor thread, temperature tends to be steadier than conductance on the cheap rigs, @Guide.

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Building on @brown71, I carry DI and do one quick tubing flush, then pull an equipment blank and hit it with a nitrate/phosphate strip; if the blank’s at or below MDL, I sample, otherwise I keep flushing or swap to a clean line. With rotating ‘early career’ crews, this keeps stops tight without guessing — anyone else using blanks as the go/no-go?

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I often run a 60–90 s closed loop through the pump and tubing to equalize temp and purge microbubbles — like warming up a car — then do one pass through the sampling line; that usually pins conductivity and NTU quickly. For VOCs I skip the loop and stick to low-turbulence purge to avoid stripping. @agreen, have you tried logging in-line temperature as a stabilization trigger?

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