As of 4/25/97

AML scripts for Tom's statistically defined vulnerability index were written. Documentation for the script is also prepared.

As of 4/19/97

First, wells and nitrate data of Texas water Development Board's data, provided as WELLS.TXT and NITRATE.TXT, are used to recreate Tom's vulnerability defined by binomial probability of excedence in nitrate concentration criteria.

Tom left some ArcInfo Macro Language (aml) files together with the data file / document file of his dissertation in a CD-ROM. Additional aml files are created to fill the gap among commands included in Tom's aml files. It is attempted that all of Arc commands are written into aml files to make sure anybody can follow the protocol. They includes system commands to run shell scripts (sed or awk) or C/FORTRAN programs.

At this moment, Info file holding best estimate of excedence probability (counts.quad by Tom's definition) has been recreated.

As of 4/3/97

Yet another change in outline.

It didn't turn out to be easy to find six base maps for DRASTIC index. So I would forget about DRASTIC method altogether and focus only on Tom Evans' statistical vulnerability. Need a little more thinking before I start doing anything using ArcView/ArcInfo...

As of 4/2/97

Please also refer to this info!!

1. Background
• Tom Evans determined groundwater vulnerability based on archive of nitrate measurement throughout Texas.
• His vulnerability map does not match well with a map of DRASTIC index.
• He could correlate his vulnerability with rainfall, but not with soil depth, soil OC content, or nitrate fertilizer use.
2. Objective
• Find factor which can be correlated to Tom Evans's vulnerability. Six factors for DRASTIC index are checked if they can correlated with his vulnerability.
• Modify DRASTIC index calculation method so that the index resembles Tom's vulnerability by adjusting multiplier of each factor in DRASTIC.
• If time allowed, come up with a second vulnerability map using archived concentration data other than nitrate.
3. Material and method
• Tom's vulnerability, which is defined on 7.5' grid throughout Texas
• maps for DRASTIC factors
• single regression analysis of Tom's vulnerability with one of DRASTIC factors as independent variables.
• single regression analysis of Tom's vulnerability with soil properties found on STATSGO or properties that can be derived from STATSGO
• multiple regression analysis of Tom's vulnerability with six of DRASTIC factors. The coefficients can be used as weighting factor for modified DRASTIC index.
• Statistical vulnerability following Tom's method but using other contaminants.
• Dr. Samuel Atkinson may be a person to contact.

As of 3/26/97

Tom Evans' paper is read except the detailed method part. It is summarized in a sub-document for nitrate concentration and vulnerability.

As of 3/21/97

Dr. Maidment indicated me that Tom Evans has done a work similar to my intention. I need to read his paper now.

As of 3/17/97

By the end of spring break, following tasks have been done.

1. Download ArcInfo export file of vulnerability map at TNRCC, and open it in ArcView. It was found that the file has single attribute which is coverage polygons, each corresponds to level of vulnerability. No data which allows calculation of the index was not posted at the site.
2. Downloaded STATSGO documentation, and browsed through to see what kind of data are available. Also made a photocopy of Charbeneau and Daniel (1993) and bury it in to a pile of stuff on my desk.
3. Read a reference by Vrba et al. What I learned from the book is included as comments in a sub-document for vulnerability map concepts.
4. Came up with some ideas of what I actually do in this project...