Synopsis: For several years, Morro Bay city staff and officials have claimed that the nitrates in the Morro Basin city wells come from fertilizer used by farmers in the Morro Valley. They allege that runoff from irrigation carries the nitrates into the Morro Basin aquifer, which is the source of the city well water.
Farmers and some Morro Bay residents disagree. Many believe that, despite claims made in a study commissioned and funded by the city, the nitrates come from sewage leaking from Morro Bay sewer lines. Two local activists reviewed the city's study and wrote a detailed response, pointing out what they believe are errors and omissions. Now, new evidence that may support the activists' and farmers' viewpoint has emerged.
While the tests run on city well water consistently show high nitrate levels, newly published test data for a nearby private well show very low nitrate levels. Yet, both well systems get their water from the same source – the Morro Basin aquifer. What could explain the difference?
Well test data recently published by the State Water Resources Control Board (SWRCB) raises new questions regarding the nitrates in the City of Morro Bay's Morro Basin well field. Very high nitrate levels have persisted in the city wells since 2002. However, test results for the water in a nearby private well on power plant property have consistently shown very low nitrate levels. That well is owned by Morro Bay Mutual Water, a PG&E affiliate.
The city wells are located in very close proximity to one another. One of those wells was chosen at random for study for this article. The SWRCB data includes well test results for both the city and the Morro Bay Mutual Water wells for the period beginning in 2002, and ending in 2009.
The nitrate levels found in the city well for that period ranged from 27 parts per million (ppm) to 100 ppm. Meanwhile, nitrate levels found in the Morro Bay Mutual Water well ranged from 1.4 ppm to 10 ppm.
The Source of the Well Water
The city's Morro Basin wells and the Morro Bay Mutual Water well draw their water from the same source, the Morro Basin Aquifer. The following diagram, is a portion of a larger diagram published in the Morro Basin Nitrate Study, which was commissioned and funded by the city. The diagram shows the location of the city wells and, in black, the boundaries of a portion of the aquifer. The portion of the aquifer not shown here extends eastward into the Morro Valley, following the paths of Morro and Little Morro Creeks.
Water in the area of the aquifer where the subject wells are located comes from several sources. According to the Morro Basin Nitrate Study, some of the aquifer's water flows in underground through the narrows - a portion of the aquifer that is about 800 feet wide, with saturated sediments about 30 feet deep. The narrows area is shown in the center-right portion of the diagram. Some of the water comes from precipitation soaking into the ground and, when Morro Creek is running, some of its water also soaks into the ground and finds its way into the aquifer. The aquifer is also subject to seawater intrusion during droughts.
The city wells are located on the west side of the narrows as shown. They are north of Morro Creek, and adjacent to Highway 1. The Morro Bay Mutual Water wells are also located west of the narrows and near Highway 1, but are south of Morro Creek, on power plant property.
The Nitrate Level Test Data
The city is required to perform regular tests of its well water and to submit its test results to state authorities. Morro Bay Mutual Water's wells are regulated by the County. They do not serve the public, so testing and reporting requirements are less rigorous, and there are fewer test results for those wells than for the wells operated by the city. However, there is sufficient data to raise questions regarding what appears to be a significant difference in the nitrate levels in the two well systems.
Year |
Well System |
Sample Date |
Nitrate level |
|
|
|
|
2002 |
City of Morro Bay |
10/21 |
47 |
|
|
11/12 |
71 |
|
|
|
|
|
Morro Bay Mutual Water |
11/20 |
10 |
|
|
12/26 |
8.7 |
|
|
|
|
2005 |
City of Morro Bay |
9/20 |
27 |
|
|
11/15 |
57 |
|
|
|
|
|
Morro Bay Mutual Water |
6/30 |
1.4 |
|
|
|
|
2006 |
City of Morro Bay |
1/18 |
47 |
|
|
6/6 |
46 |
|
|
10/17 |
49 |
|
|
11/20 |
84 |
|
|
11/27 |
86 |
|
|
11/28 |
84 |
|
|
11/29 |
80 |
|
|
11/30 |
80 |
|
|
12/1 |
77 |
|
|
12/4 |
81 |
|
|
12/5 |
81 |
|
|
|
|
|
Morro Bay Mutual Water |
12/13 |
10 |
|
|
|
|
2007 |
City of Morro Bay |
5/2 |
49 |
|
|
5/7 |
55 |
|
|
11/19 |
100 |
|
|
|
|
|
Morro Bay Mutual Water |
6/5 |
7.9 |
|
|
|
|
2009 |
City of Morro Bay |
8/4 |
69 |
|
|
9/15 |
73 |
|
|
10/6 |
72 |
|
|
|
|
|
Morro Bay Mutual Water |
7/14 |
3.3 |
Nitrate Level Problems Begin in 2002
Beginning in 2002, the level of nitrates in the city's Morro Basin wells began spiking every November. The Morro Basin Nitrate Study includes this statement, "Nitrate concentration peaks between 2002 and 2006 coincide with full scale production at the well field, which occurs annually around November during the State Water Project shutdown. Historically, nitrate concentrations in November were in decline, rather than peaking."
The chart on the right, which appears in the study, illustrates the situation. It covers the years 1954 through 2006, and clearly shows the nitrate level spikes that began in 2002.
In recent years, the city has been using its Morro Basin wells not just in November, but in other months of the year. Nitrate levels been consistently high whenever the wells are used. This ongoing contamination of the Morro Basin wells has proved costly for city residents, as the nitrates must be removed the from the water by processing it at city's desalination plant.
Residents Question the Morro Basin Nitrate Study
The Morro Basin Nitrate Study was published in December, 2007. Some Morro Bay residents immediately disputed the study's conclusion that the nitrates in the city wells came primarily from fertilizer used in agricultural operations. In April, 2008, residents Richard Sadowski and Marla Jo Bruton published a rebuttal. Their report, "The 'Morro Basin Nitrate Study': Issues and Concerns," points out a number of alleged flaws in the 2007 study, and presents the theory that the true source of the nitrates in city wells is sewage leaking from the city's dilapidated sewer system.
The Sadowski-Bruton report includes these statements of opinion: "We believe that the findings presented in the 'Morro Bay Nitrate Study' are based, in large part, upon invalid assumptions, inadequate study of major potential nitrate contamination sources, and in some cases, faulty 'science.' We believe that the study totally fails to establish any reasonable proof that agricultural operations are the primary source, or even a significant source, of the nitrates in Morro Bay wells."
Sadowski and Bruton took issue with the fact that the study failed to include tests for sewage in ground water near the wells, and apparently failed to thoroughly investigate the potential for leaking sewage to find its way into the aquifer. They stated, "Content of the Cleath report section on hydrogeology was limited to a discussion of the Morro basin covering topics such as subsurface inflow through the narrows, and stream flow seepage. We found no discussion of hydrogeology related to underground water transport outside of, and in the direction of the basin, from other parts of Morro Bay. The recharge dynamics section of the report also failed to consider the potential for exfiltrated sewage migration to the aquifer from other Morro Bay locations."
Nitrate isotope values are also an area of contention. Sadowski and Bruton's consulting chemist noted that the nitrate isotope values reported for the Morro Basin wells differed greatly from the standard values for commercial fertilizer, but were a close match to sewage isotope values cited in the study "Ground-water Quality Impacts from On-site Septic Sytems," by Dennis McQuillan. As reported by Sadowski and Bruton, in the McQuillan study, the nitrate isotope values found in sewage ranged from 7.2 to 12.1. The nitrate isotope values for the Morro Basin wells, as specified in the Morro Basin Nitrate Study, range from 7.9 to 10.0.
Standard values for commercial fertilizer differ slightly among different sources. For example, one source states that the standard nitrate isotope values for commercial fertilizer range from -4.0 to +4.0. Another, source says that the range is -3 to +2. However, both of these ranges are inconsistent with the nitrate isotope values of 7.9 to 10.0 reported for the Morro Basin wells.
Sadowski and Bruton cited a number of other issues including alleged problems with sample gathering and testing, "seemingly contradictory statements regarding nitrate concentrations," alleged "disconnects between data and conclusions drawn from it," and issues related to the study's discussion of fertilizer application.
Residents Present Their Own Theory
The Sadowski-Bruton report presents the authors' theory regarding the manner in which sewage could have found its way into city wells. In a report section titled, "Suggestions for Further Investigation," the authors note that timing of extensive excavations done as part of an MTBE cleanup effort coincides exactly with the timing of the sudden spikes in nitrate levels in city wells. The focus of the cleanup project was the site of a gasoline station that had been located on the corner of Atascadero Road and Main Street. That site, represented by the blue dot in this image, lies directly over the Morro Basin aquifer boundary and a very short distance from the Morro Basin city wells.
The Sadowski-Bruton report asks, "Could the extensive excavations and borings done here, on the boundary of the aquifer, and in very close proximity to the well field, have provided an underground path for contaminants in groundwater adjacent to the aquifer boundary (namely, exfiltrated sewage) to be pulled into the aquifer, and to the wells, when the wells are pumping? Yes, we believe so." In fact, over sixty monitoring and extraction wells were drilled into the aquifer and its northern boundary.
Sadowski and Bruton went on to say, "On page 2 of the Cleath study, it is stated, 'Ground water movement below the narrows is controlled by the city well field. When the wells are in production, a pumping depression develops that draws water radially toward the wells, including sea water drought. During non-pumping periods, ground water flow below the narrows is toward the coast at a nominal hydraulic gradient of 0.005 ft/ft.'
"Because of the remediation work between 2000 and 2002, with emphasis on preventing the MTBE from reaching the wells, along with the fact that the city was prohibited from using the wells until remediation was complete, significant amounts of groundwater containing exfiltrated sewage probably would not, in our opinion, have been able to reach the wells until 2002.
"Then, in 2002, contaminated groundwater from outside the aquifer boundary would have been pulled directly into the wells as pumping started. In our opinion, the pumping, as it drew in the contaminated water, would create a 'plume' of sewage-contaminated water that would be drawn directly to the wells. There would be some mixing with water already in the aquifer, but not enough to dilute the contaminated water to the point that nitrate levels would be in the safe zone."
The authors further state, "In summary, we consider the timing of the excavations and the timing of the sudden increase in well contamination to be too much of a "coincidence" to ignore. We see no evidence that the consultants even considered this potential source of well contamination. As previously noted, we consider the possibility of a sudden, radical increase in fertilizer usage to be highly unlikely.
"We would like to see testing of the ground water adjacent to the aquifer, and of the water in the aquifer, in the immediate region of the wells, with comparison to water IN the wells just before, and during the first few days after pumping begins in November. We believe that such testing would lead to a different conclusion than the one drawn by the consultants"
What Could Explain the Difference in Nitrate Levels in City and Morro Bay Mutual Water Wells?
Morro Bay city wells and Morro Bay Mutual Water wells are located fairly close together. Yet, tests show that the Morro Basin wells are contaminated with nitrates while the Morro Bay Mutual Water wells are not.
It has been suggested that, if the Sadowski-Bruton theory is correct and sewage is the cause of the nitrate problem, one possible reason for the difference in nitrate levels is location. The city wells are very close to the dilapidated Main Street sewer trunk line, which is allegedly a primary source of sewage pollution in the aquifer. The Morro Bay Mutual Water wells are farther from the alleged sewage source.
The usage of the wells was also suggested as a possible factor. In addition to being farther from the alleged sewage pollution source, the Morro Bay Mutual Water wells are used very little in comparison to city wells. The theory is that the wells that pump the most water are most likely to pull the pollution their direction.
According to information received from the Morro Bay City Attorney, the Morro Bay Mutual Water wells only produce about 5,500 gallons of water per day, or 2,007,500 gallons per year. The city wells produce a great deal more. For example, in 2010, the city wells produced 312 acre feet of water. That equals 101,665,512 gallons.
The fact that the city wells are closer to Morro Creek than the Morro Bay Mutual Water wells was also considered by resident researchers. It has been suggested that, if the surface water in the creek had higher nitrate concentrations than the water in the underground flows that come through the narrows, then perhaps the city wells' closer proximity to the creek might explain the nitrate level discrepancy.
However, residents report that in summer, the creek in the area of the wells goes dry. Yet, the nitrate levels in the city wells remain high. Resident researchers believe that if high nitrate levels in Morro Creek were the cause of the high nitrate levels in the city wells, then the nitrates in the wells would go down when the creek is dry. They do not.
No other theories have been advanced to explain the nitrate level differences, but Sadowski and Bruton hold to a recommendation made in their 2008 report: Test the groundwater in the immediate vicinity of the wells for evidence of sewage contamination. Some residents are currently petitioning state agencies to order independent testing in an effort to resolve the issue.
