Nitrate Migration Study
City of Walla Walla Public Works/Water Division
Objective: To find location of nitrate concentrations with respect to the City of Walla Walla’s seven wells.
Method: Made GIS maps of the seven City Wells and the 9-1-1 addresses surrounding them within a quarter-mile radius. Took these maps to the County Health Department, which holds private well records. Used the maps to find nitrate data for wells in the vicinity of, and primarily upstream from, the City wells. Also recorded previous addresses, well depths, casing types, and pump types whenever available. Collected and input into Excel the nitrate data for these private wells. Transferred this data into GIS maps, which were created with Jennifer Weston’s help. Made 7 maps with the nitrate data, for different periods of time and for different depth ranges and aquifers:
· Nitrate Data, 1991-1997, for Private Wells in the Vicinity of Walla Walla City Wells 1, 2, and 3
· Nitrate Data, 1997-2001, for Private Wells in the Vicinity of Walla
Walla City Wells 1, 2, and 3
· Nitrate Data, 1991-1997, for Private Wells in the Vicinity of Walla Walla City Wells 4, 5, 6, and 7
· Nitrate Data, 1997-2001, for Private Wells in the Vicinity of Walla Walla City Wells 4, 5, 6, and 7
· Nitrate Data for Private, Gravel-Aquifer Wells up to or exactly 110 feet deep
· Nitrate Data for Private, Gravel-Aquifer Wells more than 110 feet deep
· Nitrate Data for Probable Private Basalt-Aquifer Wells (170-460 feet deep)
Although the County Health Department does not have enough nitrate data to make the results of this study conclusive, there does not seem to be a threat of nitrate contamination to the City of Walla Walla’s wells. Less than a quarter of the pertinent nitrate tests showed nitrate levels over 5 milligrams per liter, and less than one out of 30 of the tests showed nitrate over 10 mg/L, the federal action level for nitrates.
More importantly, the concentrations do not follow any concerning patterns. Although concentrations around Wells 5 and 7 are the highest, they seem to be consistent through time, suggesting that they are the result of localized land use rather than a regional migration. Furthermore, only one of over 50 tests around these two Wells showed nitrate above 10 mg/L. Nitrate concentrations around the other five Wells are consistently less than 5 mg/L. The lone exception is an address on Kibler Road, at which two tests showed nitrate levels over 11 mg/L. This must be assumed to be a localized event, until it is further investigated.
The City Wells are very deep and draw water from the basalt aquifer beneath Walla Walla. The only place in Walla Walla where private wells are deep enough to tap this basalt aquifer is in the vicinity of Wells 1, 2, and 3. In fact, because the water table generally lies near the contact between the gravel and basalt aquifers in this part of town, most private wells in this area likely draw from the basalt aquifer. For wells known to be deep enough to be assumed to be basalt-aquifer wells, there were no nitrate concentrations over 5 mg/L, and in fact only one over 4 mg/L. Because the basalt aquifer is generally known to be inaccessible to surface water (Newcomb, Geology and Groundwater Resources of the Walla Walla River Basin Washington-Oregon, 1963), these concentrations could be assumed to be natural in water entering the aquifer in the Blue Mountains. However, since there is not an impermeable clay layer separating the gravel and basalt aquifers in this area, research into the possibility of flow between these aquifers may be beneficial.
Within the gravel-aquifer private wells, there appears to be a correlation between depth and nitrate concentration. Almost half of the wells known to be less than or exactly 110 feet deep had nitrate concentrations over 4.3 mg/L. None of the wells more than 110 feet deep had concentrations over this level. This general trend can be seen on the maps defined by well depth, as well as on the plot of well depth versus nitrate concentration (attached), which includes data for both aquifers. These results are probably due to septic tank leakage or agricultural runoff contaminating water locally and near the surface. Such contamination does not pose a threat to the municipal water supply.
Conclusions: Neither the basalt aquifer from which the City Wells draw water, nor the gravel aquifer from which many private wells draw, seems to be threatened by nitrate migration or by unsafe nitrate levels. Even marginally substantial nitrate contamination seems to be localized and near the ground surface, and can likely be dealt with only on a case-by-case basis.
Nitrate Migration Study – Internship
As I stated in my internship log early in the semester, my goals coming into this project were to learn about city and county government, especially water resource management; about groundwater systems; and about GIS maps and their applications. All of these personal objectives, in addition to Robert Gordon’s formal objectives, were met in the course of the internship.
Logistics, Successes, and Difficulties
My internship started with my calling Hal Thomas, who passed my name along to Robert Gordon at City Water Resources. Robert introduced me to Jennifer Weston, the GIS specialist, who helped me to get oriented with ArcView GIS, the primary GIS program used by the City. Robert and I then, over the next couple of weeks, figured out the general goals of the project and developed a preliminary plan of action, which Robert outlined: “Record and input information on wells that tested positive for nitrates and those that did not test. Record information as an Excel database and input into GIS. Assist County in verifying record input.”
Then, on the City computers, I began making GIS maps of the City Wells and the 9-1-1 addresses surrounding them within a quarter-mile radius. These I took to the County Health Department where I looked up these addresses among the private well records, some of which include nitrate data. Rather than strictly following the quarter-mile circles that I had developed, I used them as guidelines to find private wells within a reasonable distance of the City Wells, while concentrating especially on private wells upstream of the City Wells. I created an Excel spreadsheet, in which I recorded the nitrate test results for each well, along with the closest City Well, the address of the private well, and the nitrate test date. I also included the old address, depth of well, casing type, and pump type when available, anticipating that some of this information might help with data analysis or be otherwise useful for future reference.
I then input all of this data into the GIS maps, which I created with Jennifer Weston’s help. She helped me first to add themes for Walla Walla city limits, city and county roads, street names and addresses, and Walla Walla City wells. I then created a theme for the nitrate data, in which each point represented one nitrate test. I placed each point as near as possible to its address on the map. When there was more than one test for a single well, I put the tests in order vertically, with the newest on top. I then input all the data from my spreadsheet into the theme’s table. I organized the theme by nitrate concentration with a gradient from red to yellow, with red dots representing the highest concentrations and yellow representing the lowest concentrations.
We were primarily interested in private wells that have had nitrate tests with results of over 10 mg/L (ppm), which is considered to be the maximum safe dose. However, I only found three private well test results above this level in the vicinity of the City wells. This, in addition to the fact that I did not find many private well tests, period, for some of the City wells, made me worry about the significance of my results. Although I collected a good sampling of well data for a few of the City wells, some of the wells have very few private wells around them, primarily because they are located in City pockets. I had hoped that Robert would have ideas as to how we could either increase our numbers of data or compensate for them somehow, but instead he seemed perfectly satisfied with my inconclusive results, happy to know simply that there seems to be no threat to his Wells.
Although my results did not show immediate threats or provide conclusive results, I was able to develop some basic hypotheses about the sources and migration of nitrate around the City wells. I did so by separating the data on my GIS maps by date and then by depth. I first created two maps (one for Wells 1-3, another for Wells 4-7) showing all the nitrate test results from 1997 to 2001, and then did the same for 1991 (the first year from which I found nitrate tests results) to 1997. I did so by using a query to define my nitrate data theme as including all the tests with dates greater than 19970101 (January 1, 1997) and then those with dates less than 1997.
I then used the same method to segregate the test results by their aquifer and the depth of their well. I extrapolated which aquifer each well draws from based on knowledge of the depths of the aquifers and the depth of the wells. Only the gravel aquifer is accessible for wells in town (wells around City Wells 4-7), and I made two maps of nitrate data from this aquifer, one for tests of wells less than or exactly 110 feet deep and one for those more than 110 feet deep. I chose 110 feet because it appeared to be a natural break in the numbers.
I then made a map of nitrate data from private wells of known depth around City Wells 1-3. Because all of these private wells were more than 170 feet deep and because the water table is located near the contact between the basalt and gravel aquifers in this area, I assumed these wells to be in the basalt aquifer. Unfortunately, I did not feel that I could not use nitrate data from wells without listed depths for the maps of either the gravel or the basalt aquifer, because that would have required an irresponsible amount of conjecture on my part. My analyses of the data using these maps was aided by reading that I did about Walla Walla’s groundwater systems, in Newcomb’s Geology and Groundwater Resources of the Walla Walla River Basin Washington-Oregon, in a couple of studies provided to me by David Eaton, and in resources at the Water Division office. One particular, somewhat unrelated revelation that came out of my internship that was significant to Robert was the fact that, around City Well 1, the impermeable clay beds that generally isolate the two aquifers do not separate the gravel and basalt aquifers. This could be significant to contamination and overflow issues as the City pumps water back into the ground through Well 1.
Making these 7 maps and then making them presentable – adding borders, titles, and legends, making sure nitrate data points didn’t overlap too much, etc. – took quite a bit of time. This was exacerbated by the fact that whenever I wanted to go back and fix something small on a map, I had to redefine the nitrate data theme and reorient the map for printing. However, it was gratifying to feel myself becoming more and more comfortable and competent as I worked through these intricacies. Finally, when I declared the maps to be complete (although I still think them perhaps inevitably imperfect), I printed and trimmed copies for all the parties involved – no small feat in itself – and gave Robert the final report for my Nitrate Study, complete with these maps.
I worked on my internship as many afternoons a week as I and the facilities or people I needed were available. I had to plan around the 8 to 5 work schedule of the City and County, since I needed the computers at the Water Resources office and the card files at the Health Department. This presented some challenge, since I only have two full afternoons free. However, I generally made it to the City and/or the County one or more times a week. I usually walked to the buildings (approximately 20 minutes to either one) and sometimes got a ride back home from one of the people with whom I was working. Overall, I feel that I made a major commitment to working on the internship whenever I could and that I put enough time in to fulfill my official and personal objectives completely.
I had hoped that by working steadily on the initial stages of the project and making good progress early in the semester, I would be able to get more, different types of experience by the end of the semester. For instance, David Eaton had suggested that I might be able to help organize the Health Department’s database of well information, and Brent, from the lab at the Health Department, suggested that collecting nitrate samples should be part of the internship. However, after collecting and inputting the data, I found that, factoring in my increasingly hectic schedule later in the semester, I only had enough time to do a good job making the maps presentable and manipulating the data for final analysis and presentation. In the end, I am glad that I did not try to rush through my main project in order to do other small things, because the data manipulation and analysis were some of the more valuable parts of the internship.
Reflections, Experience, and Learning
I think that my internship was very successful overall. Once I established
all of the initial contacts, I found all of them to be friendly and willing
to help. Robert Gordon did a nice job of laying out objectives and plan for
the internship, and was very helpful in getting me started on the project. Once
I set out to find the information, I worked largely on my own, and I feel that
I established a good rapport with all of the people whom I worked around. More
centrally to the internship, I met my objectives successfully and efficiently.
Both of these successes built my confidence and enthusiasm for the project.
Although this internship started out with quite a bit of bureaucratic shuffling, I think it was very valuable for me personally. I am thrilled to have some significant experience and to have developed competence with ArcView GIS, a program that I hope to have occasion to use in the future. Contact with GIS personnel, lab technicians, and others at the City and County of Walla Walla both gave me an idea of the nature of their jobs and established contacts that I hope to utilize further while I am living in this area. I also really enjoyed learning about the complexity and utilization of aquifers and about a municipal water system – its intricacies, complications and relationship to private well systems. Certainly water supply and quality are central environmental concerns, and ones that I may be able to approach in the future from the realms of geology and/or chemistry.
This was a fairly well designed and appropriately ambitious internship. The project could be extended to investigate the primary sources of the existing nitrate concentrations or to develop a more thorough web of nitrate tests. A study of the potential for exchange between the gravel and basalt aquifers east of town could be beneficial, as could be studies of nitrate concentration trends in other areas of the county. In fact, the only major improvement that I would make to this internship would be to extend its scope – probably by extending its time frame – into other areas of experience, such as water sample collection and testing.
Robert Gordon, City of Walla Walla Water System Manager: 527-4380
As the man in charge of Walla Walla’s municipal water supply, Robert was the primary overseer of this project, which assessed threats to this supply. He was very helpful, despite his hectic schedule, and expressed much gratitude for the work I was doing. He even offered me rides home after dark, once Jennifer had left.
Jennifer Weston, City of Walla Walla GIS Specialist:
Jennifer was my main GIS tutor, and was helpful in many ways. She was very willing to answer questions or to just sit with me and advise while I worked on maps. Additionally, she took me out to see the locations of the City Wells and she gave me occasional rides to and from the City. Unfortunately, October 19 was her last day at work, and she did not expect to be replaced for a couple of months. Luckily, she prepared me well for working primarily on my own.
Walter Keyes, City of Walla Walla Public Works Department GIS Specialist: 527-4463
Walt (whose son is a freshman at Whitman, incidentally) was very helpful after
Jennifer left, even though he works in a different department at the City. The
plotter (printer) is in his office, and he went out of his way several times
to help me both with the printer and with other GIS dilemmas.
David Eaton: City/County Environmental Health Officer: 527-3290
Through David, I gained access to the County’s file of well records, which include all the nitrate data that I collected.
Jeannette Lightfoot, Environmental Health Lab at the County Health Department: 527-3290
While I looked through well record cards, Jeannette was actually eager to help me by looking up new and old 9-1-1 addresses for wells as I needed them. She helped me to find resources around the Environmental Health offices and gave me rides home a few times. Furthermore, Jeannette provided stimulating conversation while I searched through well records.