# Presentation: 279799

**Michael Rosen**
**U.S. Geological Survey**
**Carson City, NV**

**Evaluation of Ground-Water-Quality Trends Design as Part of the USGS National Water Quality Assessment Program**

**National Water Quality Monitoring Conference, San Jose, May 2006**

## Objectives of Talk

**Describe How Ground-Water Trends are Analyzed in NAWQA**
**Background  for Talks in Session**
**I****llustrate Improvements in Trend Analysis**
**Quarterly sampling analysis**
**Comparison with New Zealand National Groundwater Monitoring Program**

## Why Care about Trends in 

**Ground-Water Quality?**

**Performance of Management Practices ****(Land, Water, Chemical Use)**
**Effects of Land-Use Changes ****(Land Conversions)**
**Scientific Basis for Preventing Future Contamination**
**Prediction of Trends**

**Notes:**
The national network includes the combinations and integration of all scales of ground-water studies.
TERMINOLOGY--Major Aquifer Survey = Sub-Unit Surveys (Study Unit Surveys) SUS and expected new name for this component of NAWQA.  The Planning Team suggested “Reconnaissance Surveys,” but we wanted to take the opportunity to simplify the naming of all GW components as studies.  Also the WQ measures are comprehensive and deserve a more elevated descriptor than reconnaissance.
The NAWQA Planning Team suggested the LUS become “Studies of Recently Recharge Ground Water,” a more descriptive, but long name and impossible acronym.  The phrase “land-use” highlights the focus on nonpoint sources of these studies.

## Components of the NAWQA GW Trends Program

**Well Networks ****(generally 30 wells per study)**
**Major Aquifer Surveys ****(deep)**** ****large area**
**Land Use Surveys ****(shallow)**** ****large area**
**Agriculture**
**Urban**
**Sampling**
**Decadal (all wells)**
**Biennial (5 wells)**
**Quarterly (5 wells)**** **
**Flow System Studies**** ****(transect)**** ****small area**

## NAWQA Trend Networks

**Red outlined areas - current trend reports produced**

## Trends Reporting

**National Reports**
**Nutrients**
**Pesticides (presented here)**
**Study Area Reports**
**6 study areas (three presented here)**
**All Articles in J. Environ. Qual. in 2007 **
**VOCs Reported Separately**

## Improvements to Trend ProgramPurpose of Quarterly Sampling

**Determine intra-annual variation not related to trends**
**Allows confidence limits and error bars**** **
**Assess magnitude of long-term changes relative to seasonal and/or random changes**

## Quantifying seasonal and random variations in water quality is not easy!

**Variations due to: **
**Application and degradation rates of contaminants**
**Seasonality of the area (i.e. precipitation or river flows) not related to seasonal chemicals inputs**
**Travel times of contaminants**
**Variation in samplers **
**Other random variations?**

**Does a Subset of Wells Represent the **
**Variation in the Entire Aquifer?**

## Comparison of Concentration and Percent Change in Nevada

**Comparison of Concentration and Percent Change in Nevada**

**Axis break**

- What's the Problem?

**Variations may be larger or smaller than actual changes in a network**

**Wide range of concentrations may indicate larger variations than actually occurs**

## What's the Problem?

**Distinguishing between non-random and random variation can be difficult**
**Seasonal inputs of fertilizers and other chemicals may make natural variation difficult to determine**
**How long a record is needed before "noise" can be determined?**** **
**What happens if intra-annual variation is superimposed on non-random variation?**

## Conundrum of Sampling for Intra-annual Variation in Trend Wells

**You don’t want a trend because it confounds determining the range of noise**
**What do you do with unidirectional variation? **
**Samples are taken from wells that are likely to have land use inputs that may engender a trend response**** **
**Average of 130 wells per analyte examined**

## What Was Expected?

**What Was Expected?**

**60% < 3 detects**

## Percent Change in Nitrate Concentrations – Agricultural Wells

**13% < 3 detects**

## Percent Change in Atrazine Concentrations – All Ag wells - Detects

**43% < 3 detects**

## Percent Change in Atrazine Concentrations – Ag Wells in Corn

## Continuous Water Levels and Nitrate Concentrations in San Joaquin

**Continuous Water Levels and Nitrate Concentrations in San Joaquin**

## Lessons Learned – quarterly sampling analysis

**Quarterly data for one year does not answer the intended questions**
**Water-level data helps, but analysis must be done well by well**
**Ag land use does not explain observed seasonal variations**
**Quarterly sampling is expensive, funds could be better used elsewhere in the program**

## New Zealand example of intra-annual variation and changing land use patterns

**New Zealand example of intra-annual variation and changing land use patterns**

## Large Intra-annual Variation (at Times) But No Trends

**Large Intra-annual Variation (at Times) But No Trends**

## Lessons Learned – from Other National  Sampling Programs

**Quarterly sampling is needed for a minimum of 3 years to be successful**
**Not likely that a subset of wells will be representative of an entire network or aquifer**

## Lessons Learned – Further improvements to NAWQA Trends Assessment

**Better Nesting of Large and Small Networks**
**Incorporation of More Ground-Water Age Dating **
**Use of Ground-Water Flow and Contaminant Transport Models**