USGS Denies Data Quality Complaint On Highlands Study

Attachment: USGS Response to IQA Request for Information Correction

(http://www.usgs.gov/info qual/med nitrate concentrations groundwater nj highlands region.html)

The following provide the U.S. Geological Survey (USGS) final responses that specifically correspond to the “numbered” sections outlined in the Public Employees for Environmental Responsibility (PEER) request for information correction.

I. CHALLENGED INFORMATION DOES NOT COMPLY WITH THE INFORMATION QUALITY GUIDELINES

A) DataQuality-Lack of QualityAssurance/QualityControl (QA/QC)

Third party data, such as the Private Well Testing Act (PWTA) data, have different quality assurance standards than data collected and analyzed by the USGS. As required in the USGS’s Information Quality Guidelines (https://www2.usgs.gov/info qual/ section 111.5), the source and limitations of the PWTA data were made transparent in the report. Data used for the study was collected pursuant to the PWTA (N.J.S.A. 58:12A-26 et seq.) as implemented through the regulations at N.J.A.C. 7:9E. The act states that all water tests conducted under the law must be done by certified laboratories. The PWTA data is subjected to QA/QC control and review. The DEP regularly examines submitted data, and if a value appears to be anomalously high, the laboratory is asked to resubmit the value. Also, the submitted latitude and longitude is compared to the mapped lot and block location of the properties from which samples are taken; if they do not match, the location is corrected to the lot and block. The USGS conducted its own review of the data upon receipt and found no obvious indicators of problems. The USGS, NJDEP, and peer reviewers found the data to be of sufficient quality to meet the needs of the study. Furthermore, the use of the extensive data available from the PWTA database materially aided the investigation by improving the spatial data coverage.

In summary, the USGS considers that the PWTA data used in this report are appropriate in quality and geographical distribution to be used for estimating nitrate concentrations in the study area .

B) Data Reliability

1. Basic hydrogeological gaps violate Information Quality Guidelines

Where hydrogeological data were needed for identifying the explanatory variables. only NWIS data, which had the needed information, was used (page 11 of the report). Analysis of the NWIS data did not find well depth to be an important predictor, most likely because most wells are of similar depth and sampling recently recharged water. Although the construction details, including the depth, of the wells in the PWTA data base are not explicitly known, homeowner wells can be reasonably assumed to be shallow. As such, the water samples from these wells can also be reasonably assumed to represent the water quality of the surficial aquifer and can be related to land-surface characteristics. The NJDEP provided the 2000 ft by 2000 ft grid in which each well resides, and its use was determined by appropriate USGS officials to be sufficient for the needs of this study. The absence of hydrogeologic information for the private wells in the PWTA data base did not prevent the USGS from accurately quantifying and validating statistical relationships between land-surface characteristics and nitrate concentrations.

2. “Method Detection Limit” and non-detect values are not credible or reliable

As stated in the report 23 percent of the samples were nondetects and MDLs ranged from 0.05 to 10 mg/1 (page 9). However, less than one percent of the wells (152 wells, page 9 of report) had MDL values that were greater than 0.5 mg/1. More importantly, only five non-detect samples had MDLs above 1.0 mg/1. Thus almost 99.9 percent of the non-detects had MDLs of 1.0 mg/1, or less, which is well within the acceptable range required by the PWTA, as well as the EPA methods cited by PEER. This is well within the normal range of values seen in numerous studies conducted by the USGS. Based on the above, and other QA criteria required by DEP, the data were found to be acceptable for use in the analysis.

Concerns about how different methods of estimating non-detects would impact results were addressed appropriately in the report (page 21) by the use of four different methods for analyzing non-detects. No method produced median nitrate concentrations that were substantially different from any other.

C) Spatial Bias

The spatial bias of well locations is due to the fact that all the wells in PWTA data base are from areas containing homes and therefore are rarely located in forested areas. This was acknowledged in the report. To minimize bias, logistic regression was used to make predictions of median nitrate concentration. In other words, there is bias in the data, but the method used to estimate median nitrate concentrations was designed to minimize bias (see citation by Greene and others, page 25).

1. NJ PWTA data correlate with land use and anthropogenic loadings

The stated objective of the report was to quantify median nitrate concentration in the highlands region, and selected subregions. Although this information was to be used for regulatory purposes USGS did not cite DEPs methodology for developing septic standards because it was not relevant to the report objectives.

This investigation was designed to minimize the acknowledged geographical bias of well locations. A higher groundwater-nitrate concentration in areas with more urban and agricultural land use is a common finding throughout the scientific literature, and is clearly true from the raw data from the NJ Highlands regardless of what dataset is used.

The section of the report entitled “Median of measured nitrate concentrations in the NJ Highlands Region” (page 14) described in detail the median concentrations that would result if this bias was not removed. Methods used to minimize this bias were adequately addressed in this investigation and in the report (see section of the report entitled “Comparison of Median Measured Nitrate Concentrations and Estimated Median Nitrate Concentrations” on page 15).

2. Data sources located outside Highlands Preservation Area

The area of study was defined by our agreement with DEP. The objective of the study was to develop a method that could be used to define the median nitrate concentrations in administratively-defined areas of the entire Highlands Region. The Preservation Area is one such region. Each administrative region has different regulations. Median nitrate concentrations were estimated for all six sub-regions to address the needs of stakeholders interested in a particular area within the Highlands. Any spatial bias in the data set was addressed by use of the regression modeling technique.