south american subbasin groundwater sustainability plan...

6/26/20

SUSTAINABLE MANAGEMENT CRITERIA FOR THE SOUTH AMERICAN SUBBASIN:

Degraded Water Quality

June 26, 2020

SASb GSPWG:

Sacramento Central

Groundwater Authority

Northern Delta

Omochumne-Hartnell

Water District

Sacramento County

Sloughhouse RCD

South American Subbasin Groundwater Sustainability Plan Development

6/26/20

Today’s Objectives

▪ Begin development of Sustainable Management Criteria (SMC) for the

South American Subbasin (SASb), a key SGMA requirement

▪ Introduce/discuss a proposed SMC development process

▪ Describe and initially discuss key sustainability indicator: Water Quality

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SUSTAINABLE MANAGEMENT CRITERIA

▪ Lowering groundwater levels

▪ Reduction in storage

▪ Seawater intrusion

▪ Degraded water quality

▪ Land subsidence

▪ Surface water depletion

Sustainable Management Criteria (SMCs) are defined locally based on basin conditions to avoid

significant and unreasonable undesirable results for six SGMA sustainability indicators.

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GSP: Must Establish Metrics for Monitoring and Managing Sustainability

Sustainability Indicators

Mo

nit

ori

ng

Minimum Threshold (MT)

Triggers

Measurable Objective (MO)

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Review of Sustainable Management Criteria Concepts

Measurable Objective

Threshold

Undesirable Result

Gro

undw

ate

r Q

ualit

y C

onc

ent

ration

Undesirable Results

Minimum Thresholds

Measurable Objectives

Consistency with Sustainability Goal

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For Selected Constituents: Design “Thermometer”

▪ Minimum Threshold – defines “unhealthy”

▪ Measurable Objective – defines “healthy”

▪ Triggers – optional tools to drive actionsMeasurable Objective (MO)

Minimum* Threshold (MT)

Triggers

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Proposed SMC Development Process

Working Group to provide input on SMC for each

undesirable result (UR)

Which undesirable results are

applicable?

What “thermometer” looks

like?

Technical team will summarize existing data and

describe options

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Sustainable Management Criteria – Degraded Water Quality

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Outline

▪ SGMA requirements

▪ Water quality regulatory framework

▪ Available data and information

▪ Sustainable Management Criteria options

▪ GSA Management Options

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SGMA Requirement

◼ §345.28 (c) (4) Degraded Water Quality.

“The minimum threshold for degraded water quality shall be the degradation of water quality, including the migration of contaminant plumes that impair water supplies or other indicator of water quality as determined by the Agency that may lead to undesirable results. The minimum threshold shall be based on the number of supply wells, a volume of water, or a location of an isocontour that exceeds concentrations of constituents determined by the Agency to be of concern for the basin. In setting minimum thresholds for degraded water quality, the Agency shall consider local, state, and federal water quality standards applicable to the basin.”

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The GSA’s Responsibility for Water Quality

▪ Coordinate with existing regulatory agencies (and programs):

▪ State and Regional Boards, Department of Toxic Substances Control, Department of Pesticide Regulation

▪ Monitoring and reporting duties

▪ For recharge/pumping projects:

▪ Consider effects on existing man-made pollution

▪ Consider effects on existing naturally occurring contaminants

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Agencies with Water Quality Responsibilities

U.S. Congress State Legislature

USEPA CalEPA: State

Water Board,

DTSC, DPR

Central Valley

Water Board,

DTSC, DPR

Federal State

Laws

Regulations

Implementation

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Considerations for SMC for Degraded Water Quality

▪ What is a “significant and unreasonable undesirable result”

▪ Constituents of concern:

▪ Review and approve shortlist of constituents to be included in the GSP

▪ Are we missing existing data?

▪ Review existing and potential future groundwater quality monitoring programs available to be used in GSP

▪ Review and discuss options to set SMC for the shortlisted constituents

▪ Thresholds

▪ Measurable objectives

▪ Monitoring and reporting

▪ Projects and management actions (if needed)

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“Significant and Unreasonable”- Defining Undesirable Results for Water Quality

To be discussed:

▪ Adverse effects on drinking water uses

▪ Adverse effects on irrigation water uses

▪ Adverse effects on environmental uses

▪ Other adverse effects?

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What is the current state of WQ monitoring in the SASb?

▪ Need to design a SGMA designated monitoring network

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Municipal Wells Historical WQ collection locations

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Existing Groundwater Quality Monitoring Programs and Networks

▪ Public water supply (PWS) wells

▪ Monitored regularly for key water constituents

▪ State small public water supply wells

▪ Monitored regularly, but less frequent than PWS wells for some water constituents

▪ Domestic wells

▪ Only sporadic monitoring, if any

▪ Agricultural/irrigation wells

▪ Only sporadic monitoring, if any

▪ Monitoring wells

▪ At contamination sites to guide/assess remediation

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Existing Water Quality Data Repositories

▪ SWRCB GAMA Groundwater Information System

▪ County environmental health department

▪ Public water supply systems

▪ USGS (NWIS)

▪ U.S. EPA (STORET)

▪ California DWR

▪ California DPR

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California Water Quality Regulations pertinent to Groundwater in SASb

◼ Central Valley Basin Plan for Sacramento-San Joaquin Basin: Water Quality Objectives

◼ Maximum Contaminant Levels to protect domestic and MUN use

◼ WQOs for groundwater do not require improvements over naturally occurring background concentrations

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Maximum Contaminant Levels (MCLs)

To protect drinking water

◼ Primary MCLs – e.g. Nitrate, Arsenic

◼ Not-to-exceed standards to protect human health

◼ Secondary MCLs – e.g. Iron, Manganese

◼ Non-enforceable guidelines to achieve consumer acceptance (e.g. taste, odor, or color)

◼ May have a range of acceptable values (e.g. Recommended, Upper, Short Term)

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Approach to developing preliminary list of Constituents of Concern

▪ Constituent has an MCL or other human health-based notification level

▪ Consider data from the historical record (e.g., 30 years)

▪ Focus on water quality parameters confirmed by multiple measurements

▪ Constituent either (a) shows exceedances of a threshold, (b) shows a strong likelihood of exceeding a threshold, or (c) is commonly addressed in other GSPs.

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SASb: Data considered for this preliminary assessment

◼ Total number of wells

◼ 4,134 wells with water quality data

◼ 3,496 wells with water quality data from 1990-2020

◼ Parameters

◼ 274 unique analytes

◼ Time period (earliest to latest)

◼ 8/27/1952 – 3/26/2020

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Constituents of Concern Shortlist

▪ Screen parameters down to a reasonable number for further analysis and for setting thresholds and measurable objectives▪ Nitrate

▪ VOCs

▪ TDS

▪ PFAS

▪ Iron

▪ Manganese

▪ Arsenic

▪ Hexavalent Chromium

▪ Other Basin-specific analytes ?

▪ Other draft GSP examples

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MCLs for selected Constituents of Concern

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Constituent Units Applicable

Regulation

Regulatory Threshold

Arsenic µg/L Primary MCL 10

Hexavalent Chromium as

Total Chromium

µg/L Primary MCL 50

Iron, Total µg/L Secondary MCL 300

Manganese, Total µg/L Secondary MCL 50

Nitrate mg/L as N Primary MCL 10

TDS mg/L Secondary MCL 500 (Recommended)

1,000 (Upper)

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MCLs and NLs for selected Constituents of Concern

Constituent Units Applicable Regulation Regulatory Threshold

VOCs mg/L Primary MCL 0.005 and up

PFOA ppt Notification Level* 5.1

PFOS ppt Notification Level* 6.5

* Nonregulatory, precautionary health-based measure for concentrations of chemicals in

drinking water that warrant notification and further monitoring and assessment.

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Background on Constituents of Concern Found in GW

▪ Nitrate – Nitrogen is very prevalent in the earth’s crust; nitrates are found in groundwater as a result of the applications of nitrate-containing fertilizers, feedlot discharges, treated and untreated sewage, and emissions from industrial processes; nitrates/nitrites affect the oxygen carrying capacity of hemoglobin, thyroid gland function, and vitamin A retention.

▪ TDS - Concentration of all dissolved salts in water, which can accumulate in groundwater due to agricultural, municipal, and industrial uses. In the SASb, elevated TDS is thought to be associated with upwelling of poor-quality water from >2,000 ft.

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Background on Constituents of Concern Found in GW

▪ Related to landfills, wrecking yards, military installations, and research facilities. Solvents, with consumer and industrial uses such as degreasers, paint removers, and cleaning agents, are among the VOCs detected in groundwater. Gasoline compounds and additives are another class of VOCs that are sometimes detected in groundwater. Leaking underground gasoline storage tanks are also a commo source of gasoline VOCs to groundwater.

▪ Per- and polyfluoroalkyl substances (PFAS) are a large group of human-made substances that do not occur naturally in the environment and are resistant to heat, water, and oil. The four major sources of PFAS are: fire training/fire response sites, industrial sites, landfills, and wastewater treatment plants/biosolids. Once in groundwater, PFAS are easily transported large distances and can contaminate drinking wells.

VOCs PFAS

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Background on Constituents of Concern Found in GW: Naturally Occurring

▪ Arsenic - Arsenic is found in groundwater predominantly due to natural sources. It may also be present in localized environments in high concentrations as a result of specific releases, such as from mining and chemical spills.

▪ Hexavalent Chromium (Chromium-6) - Hexavalent chromium has been detected in groundwater in the SASb. It is naturally occurring in some areas and is also commonly associated with industrial sites where wood treatment or metal plating solutions were used.

▪ Iron - Abundant element in the earth’s crust that is found in groundwater in its dissolved form; concentrations can be elevated due to mining operations, industrial waste, and corroding metal.

▪ Manganese - Occurs naturally as a mineral from sediment and rocks or from mining and industrial waste.

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What choices does the GSA have to make?

▪ Selection of Constituents of Concern (COCs)

▪ Metrics (thresholds, measurable objectives)

▪ Monitoring Network (where and when to monitor)

▪ Implementation Actions

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What Metric to Use for the “Thermometer”

Options:

• Averages

• Medians

• Statistical trends over time

• Number of wells with exceedances

• Volume fraction of groundwater basin with exceedances

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Example Dataset

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What Metric to Use for the “Thermometer”

Options:

▪ Average

▪ Median

▪ Statistical trends over time

▪ Number of wells with exceedances

▪ Volume fraction of groundwater basin with exceedances

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6/26/20

What Metric to Use for the “Thermometer”

Options:

▪ Averages

▪ Medians

▪ Statistical trends over time

▪ Number of wells with exceedances

▪ Volume fraction of groundwater basin with exceedances

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Example MCL

Example Dataset

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What Metric to Use for the “Thermometer”

Options:

▪ Averages

▪ Medians

▪ Statistical trends over time

▪ Number of wells with exceedances

▪ Volume fraction of groundwater basin with exceedances

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Example MCL

Example Dataset

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Groundwater Quality in the SASb▪ Historical Conditions for the Constituents of Concern (COCs)

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Preliminary Constituents of Concern (Shortlist)

▪ Nitrate (as N)

▪ VOCs

▪ TDS

▪ Additional COCs?

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▪ Iron

▪ Manganese

▪ Arsenic

▪ Hexavalent Chromium

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Delineating “Shallow” and “Deep” Aquifer

▪ Initial delineation of Shallow vs. Deep Aquifer chosen as 300 ft below ground surface (BGS) ... easily adjusted with additional input from Working Group

▪ 2006 GMP delineation = 200–300 ft BGS

▪ SacIWRM layer 1 = ~185 ft BGS

▪ South County domestic wells typically 100–250ft deep

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Nitrogen Exceedances Shallow vs. Deep Aquifer

36* *

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*Wells selected based on the greatest number of measurements during the longest period of record. Non-detect data not included. In instances of multiple measurements

at the same location on the same date, the highest concentration was retained, and others removed.

0

2

4

6

8

10

12

1990 1995 2000 2005 2010 2015

Nit

roge

n -

mg/

L

Nitrogen (mg/L) - GAMA, CDPH - Shallow Aquifer (<300 ft. depth)*

MCL (10 mg/L) 3410023-010 3410033-003 3410010-010 3410010-012

3410023-003 3410023-006 3410033-009 Linear (3410023-010) Linear (3410033-003)

Linear (3410010-010) Linear (3410023-003) Linear (3410023-006) Linear (3410033-009)

MCL = 10 mg/L

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0

2

4

6

8

10

12

1990 1995 2000 2005 2010 2015

Nit

roge

n -

mg/

L

Nitrogen (mg/L) - GAMA, CDPH - Deep Aquifer (screen begins >300 ft bgs)*

MCL (10 mg/L) 3410015-020 3410015-022 3410010-002

3410010-021 3400375-001 Linear (3410015-020) Linear (3410015-022)

Linear (3410010-002) Linear (3410010-021) Linear (3400375-001)

*Wells selected based on the greatest number of measurements during the longest period of record. Non-detect

data not included. In instances of multiple measurements at the same location on the same date, the highest

concentration was retained, and others removed.

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*Non-detect data not included. In instances of multiple measurements at the same location on the same date,

the highest concentration was retained, and others removed. Only includes measurements from wells that are

definitively located in either the shallow or deep aquifer.

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TDS Exceedances Shallow vs. Deep Aquifer

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*Non-detect data not included. In instances of multiple measurements at the same location on the same date, the highest concentration was

retained, and others removed. Only includes measurements from wells that are definitively located in either the shallow or deep aquifer.

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As Exceedances Shallow vs. Deep Aquifer

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*Non-detect data not included. In instances of multiple measurements at the same location on the same date, the highest

concentration was retained, and others removed. Only includes measurements from wells that are definitively located in either the

shallow or deep aquifer.

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PFAS Concentration (all wells)

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Includes:

11ClPF3OUDS

9ClPF3ONS

ADONA

HFPA-DA

NETFOSAA

NMEFOSAA

PFBSA

PFBTA

PFDOA

PFDSA

PFHA

PFHPA

PFHPSA

PFHXSA

PFNA

PFNDCA

PFNS

PFOA

PFOS

PFOSA

PFPA

PFPES

PFTEDA

PFTRIDA

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*Non-detect data not included. Includes all well data. Data downloaded from GAMA May 22, 2020 (https://gamagroundwater.waterboards.ca.gov/gama/datadownload.asp)

**Notification Level

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Example SMC Option A Nitrate: Threshold = Primary MCL

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Triggers

Threshold (MT)

Measurable Objective (MO)

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Example SMC Option B Nitrate

▪ Long-term (30 year) trend

▪ Is either negative (downward)

▪ Or does not increase by more than 0.1 unit-per-year over the current (1990-2020) trend

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Measurable Objective (MO)

Threshold (MT)

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Monitoring Network

▪ Who Measures, When/Where to Measure

▪ Options for GSP:

A. GSA uses public supply wells and contaminant site monitoring well data reported by to SWRCB under existing WQ monitoring program

B. Option A, PLUS expanded ambient monitoring network to address data gaps

C. Other ideas?

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Where to Measure (monitoring network)

All well locations where WQ data have been collected since 1980 (GAMA).

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Where to Measure (monitoring network)

Municipal Supply Wells (SACIGSM)

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Where to Measure (monitoring network)

▪ Additional considerations: existing plumes (2006 GMP)

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Implementation – Potential Commitments in GSP

▪ Monitoring (COC-specific)

▪ Reporting

▪ Database Management

▪ Coordination with Regulatory Agencies (as-needed)

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Key decisions/Needed Input

▪ Think about what’s important in the basin - Are we missing any important COCs?

▪ Need to determine threshold (maximum) and measurable objectives – triggers?

▪ What, where, when, how, and who will measure: do we have data gaps in the current existing monitoring networks? Consider cost implications

▪ Implementation Plan

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Questions?

Thank you!

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