Vulnerability Assessment of Missouri Public drinking Water to Chemical Contamination

Introduction



The Vulnerability Assessment of Missouri Drinking Water to Chemical

Contamination project was implemented in 1991 by the Missouri Department of

Natural Resources (MDNR).  MDNR's Public Drinking Water Program (PDWP)

contracted with the Center for Agricultural, Resource and Environmental

Systems (CARES) to conduct this assessment.  The project is designed to

determine which, if any, public water supplies are threatened by any

chemicals being tested under the Safe Drinking Water Act.



Under Phase II of the Safe Drinking Water Act, the United States

Environmental Protection Agency (EPA) required that all public drinking

water systems be routinely monitored for contaminants beginning January 1,

1993.  If it can be determined that a selected chemical parameter is not

detected in an area which would affect a water supply, where detected is

defined as used, stored, manufactured, disposed or transported regardless

of amount, then the water supply need not be tested for that chemical.  If

this is the case, that system will be granted a use waiver, meaning that

the state will not test for that chemical.  There are considerable

cost-savings to be realized if use waivers can be granted.



During the first monitoring period (1994-1995), waivers were issued for 43

synthetic organic chemicals (SOCs).  The number of SOCs allowed waivers was

increased to 54 for the 1996-1998 monitoring period.  Because use waivers

are granted based on the spatial relationship between drinking water

sources and contaminant sources, accurate positional data needed to be

collected for those items.  A geographic information system (GIS) was used

to store and analyze this information in a spatial context.  A major

objective of this study was to collect as much information from existing

data sources as possible and as quickly as possible.  Therefore, nearly all

of the information collected for this project was obtained second-hand from

other sources.





Water Sources



Water sources, as defined for this study, are the points where water is

drawn from a river, lake or aquifer for use in a public water supply.  A

primary focus of our efforts was the development of the water source

layers.  These layers, containing wellheads, impoundment intakes, river

intakes and drainage basins, were created in-house or obtained from state

and federal agencies.  The water source layers were then inspected by MDNR

regional office personnel in the spring of 1993.  Since these personnel

routinely inspect Missouri public drinking water supplies, their knowledge

of these locations is exceptional.  The updated water source information

was mapped on 1:24,000 scale USGS topographic quadrangles at the regional

offices and then entered into the GIS.  Available attribute information,

provided by MDNR's Public Drinking Water Program, was associated with these

layers.  These layers are continually updated as new water sources are

developed or more accurate information becomes available.  For the first

monitoring period, only the community (i.e.  cities, subdivisions, mobile

home parks) and the non-transient non-community (i.e.  schools, large

businesses) water supply systems were considered for water source mapping.

For the 1996- 1998 monitoring period the transient non-community systems

(i.e.  parks, restaurants) were added Private water sources were not

considered in this study.



The information is stored in the GIS in the form of geographic data sets or

layers.  The wellhead layer contains 3497 public wells and their attributes

(i.e.  well depth, casing type, etc.).  The majority of the wellheads are

located in the Ozarks and Southeast Lowlands of Missouri.  Naturally poor

ground water quality prohibits a heavy reliance on ground water for

drinking water in other areas of the state.  The surface water impoundment

layer contains 107 points representing the intake locations for systems

which rely on lake water.  The majority of the systems which rely on lake

water are located in northern and western Missouri.  The final layer

represents the systems which use river water.  The majority of the 55

intakes are located on the Mississippi and Missouri rivers and on the major

streams in the Grand and Osage river basins.





Contaminant Sources



Contaminant sources, as defined for this study, are the points or areas

where existing databases indicate the presence of a chemical contaminant.

Incorporation of contaminant data into the GIS proved to be the most

difficult task.  These data usually contained very precise information

about what contaminants were found at a site and who was responsible, but

the quality of the locational information was often poor.



Ninety-eight state and federal data bases were reviewed for contaminant

information before the final use waiver analysis was performed.  Example

data bases include the EPAs Toxic Release Inventory (TRI) and the Missouri

Emergency Response Commissions Tier II Data Base.  The contaminant

information was broken into two separate types, contaminant sites and

pesticide dealerships.  The contaminant sites were the locations at which

certain chemicals were known to exist.  The pesticide dealerships were

those businesses which were licensed by the Missouri Department of

Agriculture to distribute restricted use pesticides.  Information about

contaminant sites was extracted from the databases and entered into

Microsoft Excel, a spreadsheet program.  The small amount of data with

coordinate (lat/long) or map information was readily converted to the GIS.

The majority of the contaminant records, however, contained only address

information, often appearing as a rural route address or post office box

number.



To locate these contaminant records with missing or inadequate positional

information, we relied heavily on local knowledge.  For instance, while the

water source locations were being verified at the MDNR regional offices,

the contaminant site records were also reviewed.  The regional office

personnel were familiar with their respective territories and were able to

assist CARES with the task of locating the contaminant sites.  Additional

information about the locations of contaminant sites was provided by the

Pesticide Use Investigators for the Missouri Department of Agriculture.

All of the contaminant source information was also mapped on the 1:24,000

scale USGS topographic quadrangles and transferred to the GIS.



Of the contaminant site records collected to date, 88% have been

geographically located.  At this time, the contaminant site layer contains

nearly 1400 points representing the information collected on the 54

chemical contaminants included in the study.  Each point contains a site

code serving as a link to the chemical contaminant files.  The contaminant

sites tend to be more concentrated in the urban areas and less so in rural

areas.  Even though this layer is being continuously updated, the basic

distribution of contaminant sites remains the same.



A second contaminant source layer represents Missouri's licensed pesticide

dealers.  This information is included as an indication of potential

contamination even though specific chemicals at dealership locations are

not known.  At this time we have been able to locate 1433 dealerships out

1680.





Spatial Analysis



The final parameters for the use waiver analysis were developed from EPA

and MDNR guidelines and account for the capabilities of the GIS.  These

parameters were designed to present a conservative list of the systems

which needed to be tested for the possible presence of studied chemicals.

The analysis reporting was divided into surface and ground water systems.

Parameters for the wellhead reporting were as follows:



1) A one-quarter, one-half, and one mile radius around each wellhead were

     searched for contaminant sites and pesticide dealerships.  Any

     contaminant sources found within those radii were reported to PDWP.

     (The PDWP requested that the results of the three radii analysis be

     reported, but it was decided that the half-mile radius would be used

     to determine the issue of the use waiver.)



2) Each highway and railroad within 500 feet of a wellhead was recorded.

     This gives an indication of the threat posed by the transport of

     chemicals near the wellhead.



3) The percentage of the county planted in corn, soybeans, wheat, sorghum,

     tobacco, cotton and rice was listed for each well as an indication in

     the threat posed by agricultural chemical use within that county.



4) The surrounding geographic characteristics were also reported.  These

     include land cover (LUDA/LULC), soils (STATSGO) and geology (general).

     This information was provided as an indicator only, as the data was

     too generalized to be properly used in site specific analysis.



The parameters for the systems relying on surface water were as follows:



1) Any contaminant sources found within a surface water drainage basin

     caused the associated intake(s) to fail use waiver analysis for those

     contaminants.



2) Transportation corridors passing through a drainage basin were noted as

     an indicator of the threat posed by transport of chemicals within the

     basin.



3) The percentage of the county planted in the same seven crops listed

     above were listed as an indication of agricultural chemical use within

     the drainage basin.



4) The surrounding geographic characteristics were also reported.  These

     include land cover (LUDA/LULC) and soils (STATSGO).  This information

     was provided as an indicator only, as the data was too generalized to

     be properly used in site specific analysis.



Many of the rivers which supply water to systems in Missouri have their

headwaters outside the state.  To fully evaluate the potential for

contamination within those drainage basins, we would have to collect data

for large areas outside of the state.  For example, the Mississippi and

Missouri River drainage basins cover large portions of the United States.

Because it is not realistic to collect data for those areas, we have

analyzed only those river intakes which drain areas entirely within the

state.





Results



The results of the use waiver analysis indicate which systems may be

affected by the use of a chemical near a water source.  As anticipated, the

results show that significant savings can be realized by applying GIS

technology to this problem.  The analysis has been performed twice, once

for the 1994-1995 monitoring period and then later for the 1996-1998

monitoring period.  The 1994-1995 period included only 43 SOCs and a subset

of the water sources in Missouri.  The cost of testing all wellhead systems

for those 43 contaminants without issuing use waivers was estimated over

$16 million.  Through this analysis, the state was potentially able to save

over $14 million in testing costs during 1994-1995.  For the 1996-1998

analysis the number of water sources was increased by 50% and eleven new

SOCs were added to the waiver list.  This increased the total cost of

monitoring for the period to more than $24 million.  Once again, the GIS

analysis indicated that costs could be dramatically reduced, estimating

that less than $3 million need be spent.





Table 1.  Estimated Cost Savings (in Millions).  

_________________________________________________

Period 			1994-1995 	1996-1998

Cost Before Analysis 	  $16.06 	  $24.13

Cost After Analysis 	   $1.85 	   $2.87

Total Savings 		  $14.21 	  $21.26





Several interesting trends were apparent from our analysis.  Of the

population in Missouri which is served by public water, nearly

three-fourths depends on surface water.  However, of the nearly 3700 water

sources in the state, only 162 were surface water sources.  The majority of

the groundwater sources are located in the Ozarks, where agricultural

cropland is very rare due to topography and soil structure.  The use of the

chemicals in this study, most of which are agricultural, is already very

limited due to these conditions.  Therefore it should not be surprising

that most of these sources were granted waivers.



By contrast, most of the surface water sources drain areas in the heavily

agricultural northern and western portions of Missouri.  This study

indicated, and monitoring has shown, that these water sources do have a

problem with agricultural chemicals.  The analysis indicated that

seventy-five percent of the surface water sources were in basins which were

three-fourths or more agricultural.  Monitoring has indicated the presence

of these chemicals in most surface water supplies in Missouri, although

exceedances of the MCL are found in only a few.  Because of this situation,

CARES is currently investigating several surface water models which may

assist in the evaluation of the dynamics of these watersheds.  By combining

the function of a model with the resources of a GIS, we feel that the

utility of both can be greatly enhanced, and that our understanding of the

problems faced in these watersheds may be correspondingly increased.





Summary



To date the investment made by the state in the Vulnerability Assessment

project has had a many fold return.  The state has realized up to $35

million is savings for an investment of only about $500 thousand.  Many

data sets have been developed as a result of this project, which have

already benefited MDNR and other agencies.  In addition, the basic

framework has been established for future assessments, which are required

on a regular basis by the EPA.



GIS technology and methodologies have proven to be greatly beneficial in

this project.  CARES and many other entities in Missouri are currently

seeking other applications of this technology.  We feel that many fields in

the state, including resource management and agriculture, may be able to

achieve similar results.