The Relationship of Land Use and Groundwater Quality: A Case Study of Rhode Island

The quality of groundwater used for drinking is critical to consumers. Due to the nature of groundwater flow, pollution source control is important for groundwater protection. Point and nonpoint pollution sources are closely related to land use. The pollution sources that originate from particular land uses must be identified and controlled to prevent degradation of groundwater quality. This research is a study of the relationship between groundwater quality and land use in Rhode Island State. Water quality data were collected from twenty-one public drinking water wells and land use data were interpreted from air photos. Water quality data and land use data from 1970 and 1988 are compared to analyze the change of land use and change of groundwater quality. The study areas are within a 1,000 foot radius around each well. Land use types include commercial/industrial, residential, undeveloped, and agricultural land. Road systems are also considered as a factor in this study. A computerized Geographic Information System (ARC/INFO) has been applied in the study. Several statistical methods have been used to analyze the relationship between land use and groundwater quality. The water quality data in 1988 indicate that nitrate and chloride do not pose a threat to groundwater in Rhode Island. However, sodium levels are likely to cause water quality problems at some public drinking water wells. The analysis demonstrates that the nitrate, chloride, and sodium concentrations in groundwater in 1988 were greater than that in 1970. This indicates that groundwater among the study wells has degraded over the study period. The study determined that undeveloped areas around study wells decreased significantly from 1970 to 1988. The result shows that most new development in these area had converted undeveloped land into residential, commercial, or industrial land. The study has found that the areas of residential land use and surface water are related to increases in the levels of chloride and sodium concentrarions in the wells. Nitrate concentrations in the wells are closely related to increased areas of residential land and paved light duty roads. It can be concluded from the research that urbanization has an impact on groundwater quality. Attention should also be given to the area beyond the 1,000 foot limit. Further studies will need to include more independent variables and more valuable findings are expected by increasing the


CHAPTER 1 IBTRODUCTIOR
The quality of groundwater used for drinking is critical to consumers.
Due to the nature of groundwater flow, it is very difficult and possibly not practical to cleanse contaminated groundwater. Therefore, response to contamination incidents after they occur is not an adequate solution to the problem of groundwater pollution.
Pollution source control is important for groundwater protection.
There are two major pollution sources affecting the quality of groundwater: Point sources and non-point sources. Both pollution sources are closely related to land use.
The pollution sources that originate from particular land uses must be identified and controlled to prevent degradation of groundwater quality. It is a matter of considerable urgency to examine the relationship between land use and groundwater quality. A serious concern is how the urbanization effects the quality of groundwater in the state. This research project is a study of the relationship between water quality of selected public drinking water wells, and land use surrounding the wells, in the State of Rhode Island.
Chapter two will provide a broad background of hydrologic circulation, groundwater as a resource and the potential pollution sources of groundwater. Groundwater is an important portion of the earth's water resources. Human activities become more varied because of groundwater.
However, pollutants generated by human activities are endangering the groundwater quality.
Chapter three will discuss the existing groundwater quality in the State of Rhode Island and the change of groundwater quality from 1970 to 1988. The analysis is based on data from twenty-one public drinking . water wells.
2 Chapter four will examine land use typies surrounding the sample wells within 1,000 foot radius. The writer will first clarify the concept of contributing area of a pumping well, then determine the study area for this research, and final1y, identify and analyze the land use patterns within the study areas. A computerized Geographic Information System/(ARC/INFO) at the University of Rhode Island was applied for the study.
Based on the findings from the previous chapters, Chapter five will go further into the relationship between groundwater quality and land use type. Statistic techniques are used to identify the relationship.
Chapter six will summarize the research project and recommend further studies. This is a preliminary study of the factors of groundwater pollution. It is also an effort of applying GIS into groundwater protection and land use study.
More valid findings are expected with studies in depth.

Hydrologic Circulation
Hydrologic cycle refers to the circulation of water within the total earth system: atmosphere, hydrosphere, and lithosphere. The atmosphere is the gaseous envelope above the hydrosphere. The hydrosphere consists of the water bodies which cover the surface of the earth. The lithosphere is the solid rock environment below the hydrosphere.   .  The groundwater storage accounts for 0.6 percent of total water resources and half of it remains within a depth of 2,600 feet or less, which can be economically extracted with the present drilling technology (Raghunath 1987).
Among the available water resources, groundwater storage is about thirty times more than that from streams and lakes.
Groundwater provides water supply to industries, agriculture, municipalities and many other consumers.
People use groundwater because of its convenient availability near the point of use, its excellent quality, and its relatively low cost of development (Todd 1980 The studies of erosion and sedimentation, contaminated runoff, and soil loss indicate that management of erosion and sedimentation, and waste management controls on farm lands will be necessary in order for certain watersheds to achieve their designated water quality standards (Myers 1988).

Road Deicing Practices
Salt applied to snow-or ice-covered roads is a source of chloride and sodium to groundwater. Many streams receive municipal and industrial wastewater and runoff. Seepage of such water into groundwater may adversely affect groundwater quality. The surface water recharge to groundwater may be included by a pumping well, as indicated in Figure 2.3 (Todd 1980). 2.4.6.

Landfill
Many wastes of animal, municipal, industrial, or agricultural origin are applied on the land for disposal purposes, which leach into groundwater.
The interest in utilizing land as a terminal receiver for disposal of wastes has focused considerable attention on the potential pollution source contributions from such land application sites.

Municipal and Household Activities
Groundwater quality is threatened by miscallaneous municipal and household activities. Underground storage tanks present a threat to groundwater because of their propensity to leak. Pesticide and fertilizer contamination of water is not limited to agriculture. Spraying of pesticides and herbicides in parks, trees, golf courses, and along roads and rights-of-way is common. This is frequently done routinely without consideration of actual need or potential impact on groundwater.
The use and improper disposal of household cleansers, automotive products, and lawn and garden products may also cause groundwater pollution.
With the increasing urbanization in Rhode Island, the amounts of fertilizers and pesticides applied to home lawns have become a significant concern. Data show an increase or fertilizer use in Rhode Island from roughly 13,000 tons/year in 1980 to over 20,000 tons/year in 1986.
However, farm type fertilizer usage constituted less than 2,000 tons/year in 1986 ( Figure 2.4).

I Farm Use
Source: RIDEM/OEC 1988 D Home Use

CHAPTER 3 GROUIDVATER QUALITY I• RHODE ISLA8D
Groundwater is a limited natural resource that is crucial to society. Drinking water supply is determined by water storage and water quality.
Recently, many studies have reported the degradation of groundwater quality. Several public water systems which formerly relied on groundwater, in whole or in part, as a supply source, have switched to reliance on surface water supplies due to increasing problems with contamination (Concern (a) 1988).

As of
February 1986, nine public water system wells in Rhode Island had to be taken out of service because of groundwater contamination (RIOSP 1986 Furthermore, among the twenty-eight wells, seven pairs were located less than 1,000 feet from each other. Seven wells were dropped randomly because of the requirement of land use study. As a result, the sample population consisted of twenty-one wells. 21 In spite of the small sample size, the twenty-one wells are located in more than ten different groundwater reservoirs.
The nitrate, chloride and sodium concentrations from the sample wells also represent the three possible change: increase, decrease, and stable.   Well # 1970Well # 1988Well # 1970Well # 1988Well # 1970Well # 1988 Olnt>erland The sodium concentration data for the sample wells show different result.

Existing Condition
In 1970, water in one well (well 20) had 35.7 mg/l sodium, which was 15.7 mg/1 higher than the 20 mg/1 RIDEM recommended maximum concentration.
In 1988, well 20 still had the highest concentration, which was 53.9 mg/1 and the sodium concentrations from five wells were greater than the 20 mg/1 level.
The figures infer that sodium contamination of public drinking water wells in Rhode Island poses increased levels of concern among selected wells and aquifers.

1970
- The data imply that the sources contributing nitrate to groundwater may be different from the sources contributing chloride or sodium, and that chloride and sodium in groundwater may come from similar sources. It is necessary to determine whether the sample differences provide a basis for inferring actual water quality differences between the two time periods.
The c-0ncept of statistical significance helps to decide how much the sample means must differ in order for the null hypothesis to be rejected.

CHAPTER -LARD USE SURROURDIRG THE SAMPLE WELLS
After examining quality of selected constituents in public drinking water wells and finding that water quality had degraded from 1970 to 1988, the next step is to find at what extent human activities affect water quality change.
Following is a study of land use as a factor affecting groundwater quality degradation.

Definition of Related Terms
Drawdown. When pumping ~s started, the water level in the vicinity of a pumped well is lowered.   are not influenced by the pumping well, but water in this area will also naturally flow to the well. The groundwater contributing area will be distorted to extend to a greater distance than the influence area on the upgradient side, and t~ a lesser distance than the influence radius on the downgradient side.
The influence area and the contributing area are two different concepts and the latter is more important to groundwater protection. Any pollutants in the contributing area will eventually reach the well and adversely affect the quality of water obtained from the well.

Factors attecting contributing area
The shape and size of the contributing area of a pumping well is determined by geohydrologic factors and well factors as shown in Table 4.1. These factors affect the discharge from and recharge to a pumping well to some degree depending upon specific conditions at the site.
The factors are divided into two groups. The first group includes geohydrologic factors which determine the characteristics of the area where a pumping well is

Rationale ror Selecting a Method
This project is a preliminary analysis of the relationship of groundwater quality and land use for planning purposes.
Based on the following considerations, the fixed radius method is applied. In addition, the geologic nature of the glacial drift is considered. Therefore, outwash deposits are separated from till deposits within the 1,000 foot radius study area.
between groundwater and surface water.
This phenomenon has significant impact on groundwater protection. Pollutants may travel long distances through surface water and contaminate the groundwater in the well site.
Among the twenty-one sample wells, only one well does not have outwash deposit within its 1,000 foot radius area.
The study areas of ten wells are completely in the outwash deposit areas.
Undeveloped land is a major land use type.
In 1970, in average about seventy-two percent of the study area was

Siaple Linear Regression Analysis
A simple linear regression model is applied to analyze the water quality and land use data and the results are presented in Table 5.1. Previous studies have shown that nitrate in groundwater is likely from agricultural land, residential areas and some commercial and industrial activities.
For chloride and sodium, in addition to the three sources, deicing salt on road systems is a major source.
Nitrate, chloride, and sodium were dependent variables. In the first part of regression analysis, the independent variables include the area of commercial/industrial, residential, agricultural land, the length of paved light duty roads, paved heavy-medium duty roads, and the length of total paved roads within the 1,000 foot radius study area.
In the second part of the regression analysis, the area of outwash deposits is considered as a control factor. Table   5.1 shows the regression coefficients of water quality indicators and different land use above outwash deposits.   The probability of correlation coefficients equal to zero is as follows: The regression coefficients of water quality and land use above outwash deposits have higher values than the coefficients with the land use figure for the whole area, which includes both outwash and till deposits. This could be an indication that water quality may be more closely related to land use above the outwash deposits and pollutants in outwash deposits have greater impacts on groundwater quality than those in till deposits.
Therefore, the following analysis will focus on the land use above outwash deposit only.
Area of surface water bodies is considered as an additional factor which may reflect the impact of activities outside of the 1,000 foot radius area.      A high coefficient value was also found between the change of undeveloped land and the change of commercial/industrial land (r=-0.74, n=21, p:O).
At-test showed that these relations were 100 percent significant.
The correlation coefficient for residential land and industrial/commercial land shows that the two variables are also correlated (r=0.45, n=21, p<0.04).
Based-on these results it is concluded that a multiple regression analysis is not appropriate because of the autocorrelation between the independent variables. This research is an effort to assess the impacts of nonpoint sources of pollution on groundwater and to provide basic information for protecting groundwater.
This report explores the existing condition of water quality in some of Rhode Island's public drinking water wells and the relationship between land use and groundwater quality. The statistical analysis of the twenty-one sample well sites showed that there was a significant increase of residential, commercial, and industrial land within a designated groundwater contribution zone from 1970 to

1988.
Although the data in 1988 indicated that the public drinking water quality was, overall, in good condition, the concentrations of nitrate, chloride, and sodium indicated that the groundwater had degraded significantly since 1970.

\
The analysis or water quality and land use shows that residential land is providing nitrate, chloride, and sodium to groundwater. Paved light duty roads are also related to nitrate concentration in groundwater.
Areas within 1,000 feet radius around public drinking water supply wells are crucial to groundwater protection.
Nonpoint pollution sources within a 1,000 root radius circle around a pumping well provide pollutants to the well. However, they are not the only sources.
Attention should also be given to the area beyond the 1,000 foot limit. The discussion of contributing area will help to understand that the 1,000 foot radius circle may only be part or the contributing area. Pollutants from other nonpoint pollution sources in the contributing area will eventually arrive at the pumping well. The nonpoint source management plan needs to cover the entire contributing area.
The high correlation coefficients between chloride and sodium concentrations and surface water area indicate that pollutants may come from larger areas through surface flow.
Because of the close relation between groundwater and surface water, it is important to make appropriate land use plans for the watershed of surface water for the purpose of protecting groundwater.
It can be concluded from the research that urbanization has an impact on groundwater quality. This is a preliminary study of the factors of groundwater pollution. Many different variables could be considered for explaining the degra~ation of groundwater quality. Further studies will need to include more independent variables such as point source pollution components. By increasing the sample size, more valuable findings are expected.