To: Members of the Castle Rock Water Commission
From: Mark Marlowe, P.E., Director of Castle Rock Water
Title
Instrument Failure
Town Council Agenda Date: NA
Body
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Executive Summary
Castle Rock Water (CRW) had a regulatory instrument at Plum Creek Water Purification Facility which records chlorine readings every four hours, fail. Unfortunately, the design of the instrument fails with the last value recorded continuing to show on the instrument and record in CRW’s controls system (meaning everything looks good and no alarms go off), an instrument specific issue CRW was previously unaware of. While CRW has other ways and instruments in different locations to verify chlorine levels in CRW’s system are fine (i.e. the safety of the water was never in question), this instrument is an instrument that is CRW’s official regulatory monitoring point. The instrument is required to record data every 4 hours in accordance with regulations from the Colorado Department of Public Health and Environment (CDPHE). The instrument failed during two time periods (May 23 - 24 for 13 hours and May 31 - June 1 for 18 hours) before CRW’s operators were able to identify and correct the issue. As a result, CRW will be receiving two “Tier 3” monitoring violations. These violations will need to be reported in CRW’s next Consumer Confidence Report (CCR) which will be published in March of 2026. Attachment A provides the language, some of which is required by CDPHE, as well as CRW’s explanation for the public of the issue that occurred and that will be used in the CCR next year.
CRW has corrected the issue in a number of key ways:
1. CRW has added a second instrument at each regulatory monitoring point for all six water plants.
2. Operators are now required to verify each instrument’s performance every four hours in case an alarm does not go off for some other reason.
3. The control systems have been reprogrammed to alarm if a chlorine value does not change over several minutes, which would indicate a failure of the instrument.
4. Ultimately, CRW will also be replacing these instruments with a new model from a different company that does not have this issue of “holding a value” at failure.
Attachments
Attachment A: May 2025 Tier 3
Attachment B: June 2025 Tier 3