Chromium 6 (aka Hexavalent Chromium)
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Chromium 6 Detections in Soquel Creek Water District (SqCWD) Wells serving Rio Del Mar, Seascape and La Selva Beach
SqCWD has long monitored for total chromium as required by state and federal law. Testing specifically for chromium 6 began after new regulations were put into place in January 2001. Across California, chromium 6 was detected in about one-third of the public drinking water sources. At Soquel Creek Water District, chromium 6 has been detected in 6 of our 15 active water supply wells. Impacted wells draw water from the Aromas Red Sands Aquifer, which has widespread naturally occurring deposits of chromium 6 due to the local geology. Affected areas of our District include Rio Del Mar, Seascape and La Selva Beach (see more about the source of local chromium 6 deposits below.)
Regularly completed tests measure chromium 6 in SqCWD Aromas Red Sands wells ranging from 0.42 parts per billion (ppb) to 40 ppb. The highest concentration is from the one active La Selva Beach well. We currently blend this water in La Selva Beach with water from outlying wells to reduce the levels of chromium to an average of 14 ppb. The average chromium 6 concentration in Rio Del Mar-Seascape is 9.5 ppb.
Levels detected in SqCWD wells are within current State and Federal drinking water standards (maximum contaminant levels) of 50 ppb and 100 ppb, respectively, for total chromium. SqCWD is closely monitoring actions by the California Department of Public Health (CDPH) to develop a new drinking water standard for chromium 6.
Status of Drinking Water Standard for Chromium 6
The California Environmental Protection Agency’s Office of Environmental Health Hazard Assessment (OEHHA) withdrew its Public Health Goal (PHG) for total chromium in drinking water in November 2001. The decision came three months after an expert panel convened by the University of California on behalf of the OEHHA proposed additional studies be completed. The panel proposed that, until the additional studies are completed, California should continue to consider its current drinking water standard (maximum contaminant level) of 50 ppb for "total chromium" to be protective of public health. The federal standard is 100 ppb.
OEHHA and the California Department of Health Services (CDHS) [now California Department of Public Health (CDPH)] committed in March 2001 to develop the nation’s first PHG and drinking water standard specifically for chromium 6. PHGs are levels of compounds in drinking water that would not pose a significant health risk to individuals consuming 2 liters of water containing the subject constituent per day over a 70-year lifetime. PHGs are non-enforceable goals based solely on public health risk considerations. A PHG is not a boundary line between a "safe" and "dangerous" level of a contaminant. Drinking water with contaminant levels exceeding a PHG can still be considered acceptable for public consumption. None of the practical risk-management factors that are considered by the US Environmental Protection Agency (EPA) or the CDPH in setting drinking water standards (maximum contaminant levels) are considered in setting the PHGs. These factors include analytical detection capability, treatment technology availability, benefits and costs. The PHGs are not enforceable and are not required to be met by any public water system.
In late July 2011, OEHHA finalized a new PHG for chromium 6 of 0.02 ppb. This PHG for chromium 6 replaces the withdrawn PHG for "total" chromium consisting of both chromium 6 and chromium 3, an essential nutrient.
CDPH will use the new PHG to develop a chromium 6 drinking water standard. The eventual standard will be set as close to the PHG as economically and technically feasible. Legislation signed by Governor Gray Davis in October 2001 (Senate Bill 351 by Senator Deborah Ortiz) required the State to adopt a chromium 6 drinking water standard by January 2004. The legislative deadline has long passed. Development progress with the chromium 6 drinking water standard can be tracked at http://www.cdph.ca.gov/certlic/drinkingwater/Pages/Chromium6.aspx
A major study by the National Toxicology Project on the carcinogenesis of chromium 6 in drinking water has been completed at the request of OEHHA and CDHS. The report can be reviewed at http://ntp.niehs.nih.gov/files/546_WEB_FINAL.pdf
The US EPA is currently re-evaluating the federal drinking water standard for total chromium based on new chromium 6 research, and has initiated a review of its health effects. In September 2010, US EPA released a draft of that scientific review for public comment. When the human health assessment is finalized in 2011, the US EPA will determine if a new federal drinking water standard needs to be set.
Northern California Cancer Study
In August 2001, at the request of the Santa Cruz County Public Health Department, the Greater Bay Area Cancer Registry at the Northern California Cancer Center completed a review of the incidence of lung and overall cancer occurring in areas served by District wells having detected levels of chromium 6.
This analysis revealed no apparent excess of either lung cancer or overall cancer incidence among residents receiving water from wells in Rio Del Mar, Aptos, and La Selva Beach compared to the rest of the region.
Aromas Red Sands Source Water Assessment
In April 2002, a source water assessment that investigated potential contamination sources and the susceptibility of the District’s drinking water wells to identified contamination threats was completed by Todd Engineers. The study included an analysis of the probable cause of the occurrence of chromium 6 in the Aromas Red Sands Aquifer and the potential for increased concentrations of chromium 6 due to in-home reverse osmosis systems in areas using septic systems for wastewater disposal.
The study could find no man-made sources of chromium 6 and found that environmental conditions tend to favor chromium 6 production from dissolved trivalent chromium found in the local geology. These findings led to the conclusion that the occurrence of chromium 6 in the aquifer is natural.
Reverse osmosis systems can result in a significant increase in water usage depending on the type of system used. Reverse osmosis discharges to the regional wastewater treatment plant will have little impact on groundwater quality, while discharges to onsite septic systems can infiltrate groundwater. Point of use systems (treatment at the tap) will have little impact on water use or chromium 6 concentrations in groundwater due to the small amount of the water supply that is treated. Point of entry (all water flowing into the house is treated) reverse osmosis systems can more than double the amount of water used by the household, potentially overloading septic systems.
The Aromas Red Sands Source Water Assessment Executive Summary is available at the following link http://www.soquelcreekwater.org/Water_Quality/SWAP_Exec_Sum.pdf or available free-of-charge at the District headquarters office.
Local Actions
Grant funding has been received by the Santa Cruz Integrated Regional Water Management Foundation to perform a planning and feasibility analysis for the redistribution of groundwater pumping between the Aromas Red Sands and Purisima Formations near the boundary between the Central Water District (CWD) and SqCWD. This study will evaluate the potential for shifting more pumping from the Aromas to inland portions of Purisima Formation in the CWD area to better balance the pumping and avoid future treatment costs for chromium 6 removal.
SqCWD plans on initiating a formal review of potential chromium 6 treatment alternatives. This screening process will utilize District-specific water quality data and site constraints to evaluate six potential treatment alternatives based upon effectiveness, ability to implement and cost. Pilot testing of the most appropriate alternative(s) will follow. This project will likely commence in August 2011.
The available chromium 6 treatment processes are very expensive. In anticipation of installing treatment facilities at some or all of the wells with chromium 6 above the drinking water standard, the District started a Water Quality Projects Reserve, which has a current balance of $2.52 million.
In August 2011, SqCWD will begin construction on a new well which will pump water from an aquifer that has not had detected chromium 6. The Polo Grounds Well and Treatment Plant is anticipated to be online in 2012 and should be capable of providing approximately 25% of the water supply for Rio Del Mar and Seascape.
In 2007, SqCWD also reactivated the Aptos Jr. High Well after installing an iron and manganese treatment plant. This well offsets approximately 18% of water formerly produced from nearby wells with the much higher chromium 6 concentrations.
Over the next 2-3 years, SqCWD plans to complete the projects needed to be able to move water from other portions of the District to the area with detected chromium 6. These projects include two new pump stations, a new storage tank, main upgrades and several new wells.
SqCWD continues to evaluate the potential for developing a seawater desalination project with the City of Santa Cruz. This project would significantly enhance the District’s capability to deliver water that does not have detected chromium 6 to the affected communities.
